A Multi-Institutional Collaboration to Understand Neoplasia, Treatment and Survival of Snakes

Abstract

This multi-institutional collaborative study of neoplasia in snakes reviewed medical records of snakes at each facility to determine species prevalence, survival, and methods of treatment. Complete species numbers of snakes were also collected at each facility. In total, 65 species, 133 snakes, and 149 unique neoplasias were included in this study. Affected species, age, sex, and their tumor prevalence, tumor type and location, metastasis, treatment, and survival data are reported. The highest species-specific tumor prevalence was in Common or Northern Watersnakes (Nerodia sipedon) (30.8%, n = 4 of 13), Eastern Diamond-Backed Rattlesnakes (Crotalus adamanteus) (26.3%, n = 5 of 19), and Timber rattlesnakes (Crotalus horridus) (22.7%, n = 5 of 22). Malignant tumors predominated (86.6%, n = 129 of 149) with soft tissue sarcomas being the most common (30.2%, n = 45 of 149). Snakes with malignant neoplasia, metastases, or indeterminate presence of metastases were statistically more likely to die from their neoplasms than snakes having either benign neoplasia or no diagnosed metastases (p < 0.05). Gender, taxonomic family, and species of those evaluated did not significantly affect the outcome of snakes with neoplasia. Only 27.1% (n = 36 of 133) of snakes received a reported form of treatment and, for those treated, surgical excision was the most common treatment modality. There was not a significant difference in outcome based on treatment; however, surgery and chemotherapy were associated with death from a cause other than their tumor.

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Citation: Duke, E.G.; Harrison, S.H.;
Moresco, A.; Trout, T.; Troan, B.V.;
Garner, M.M.; Smith, M.; Smith, S.;
Harrison, T.M. A Multi-Institutional
Collaboration to Understand
Neoplasia, Treatment and Survival of
Snakes. Animals 2022,12, 258.
https://doi.org/10.3390/ani12030258
Academic Editor: Mathew Crowther
Received: 24 November 2021
Accepted: 18 January 2022
Published: 21 January 2022
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animals
Article
A Multi-Institutional Collaboration to Understand Neoplasia,
Treatment and Survival of Snakes
Elizabeth G. Duke 1,2 , Scott H. Harrison 3, Anneke Moresco 2, Tim Trout 4, Brigid V. Troan 1,2 ,
Michael M. Garner 5, Madison Smith 2, Sidney Smith 2and Tara M. Harrison 1,2, *
1Department of Clinical Sciences, North Carolina State University College of Veterinary Medicine,
Raleigh, NC 27607, USA; ecgraebe@ncsu.edu (E.G.D.); brigid@troan.org (B.V.T.)
2Exotic Species Cancer Research Alliance, North Carolina State University College of Veterinary Medicine,
Raleigh, NC 27607, USA; moresco2@gmail.com (A.M.); mrsmit18@ncsu.edu (M.S.); slsmit16@ncsu.edu (S.S.)
3Department of Biology, North Carolina Agricultural and Technical State University,
Greensboro, NC 27514, USA; scotth@ncat.edu
4Department of Animal Care, Denver Zoo, Denver, CO 80205, USA; timtrout@comcast.net
5Northwest ZooPath, Monroe, WA 98272, USA; zoopath1@gmail.com
*Correspondence: tara_harrison@ncsu.edu or escra.cancer@gmail.com; Tel.: +1-517-214-3112
Simple Summary:
Multiple studies have focused on types of neoplasia found in snakes, but an
overall estimation of prevalence including total populations of animals at multiple facilities has not
been conducted. Additionally, an in-depth evaluation of methods of therapy and survival of snakes
with neoplasia has not been carried out. This study calculated the prevalence of tumors in 133 snakes,
representing 65 different species, housed in six zoos and aquariums. Survival times were evaluated
to determine whether these snakes were more likely to die from their tumors versus another cause.
Treatment outcomes were evaluated to determine if the used treatment types lengthened the snakes’
life spans. Common or northern watersnakes (Nerodia sipedon), eastern diamond-backed rattlesnakes
(Crotalus adamanteus), and timber rattlesnakes (Crotalus horridus) had the highest prevalence of tumors.
Malignant (cancerous) tumors predominated, and the snakes with these tumors were significantly
more likely to die of their cancer than those with benign tumors. Thirty-six of the 133 snakes received
treatment for their tumors. There was no significant difference in survival times for those treated and
not treated. This population is a subset of the overall snake population under managed human care,
and a larger collection of snake tumor and population data could yield different results. Therefore,
additional snake cases, along with other non-domestic species, are continuing to be curated in a
database (Exotic Species Cancer Research Alliance tumor database). The goal of this data collection is
to provide data on a select population of snakes to help veterinarians gain greater understanding of
cancer types and to treat cancer in these animals.
Abstract:
This multi-institutional collaborative study of neoplasia in snakes reviewed medical records
of snakes at each facility to determine species prevalence, survival, and methods of treatment.
Complete species numbers of snakes were also collected at each facility. In total, 65 species,
133 snakes
,
and 149 unique neoplasias were included in this study. Affected species, age, sex, and their tumor
prevalence, tumor type and location, metastasis, treatment, and survival data are reported. The
highest species-specific tumor prevalence was in Common or Northern Watersnakes (Nerodia sipedon)
(30.8%, n= 4 of 13), Eastern Diamond-Backed Rattlesnakes (Crotalus adamanteus) (26.3%, n= 5 of 19),
and Timber rattlesnakes (Crotalus horridus) (22.7%, n= 5 of 22). Malignant tumors predominated
(86.6%, n= 129 of 149) with soft tissue sarcomas being the most common (30.2%,
n= 45 of 149
). Snakes
with malignant neoplasia, metastases, or indeterminate presence of metastases were statistically
more likely to die from their neoplasms than snakes having either benign neoplasia or no diagnosed
metastases (p< 0.05). Gender, taxonomic family, and species of those evaluated did not significantly
affect the outcome of snakes with neoplasia. Only 27.1% (n= 36 of 133) of snakes received a
reported form of treatment and, for those treated, surgical excision was the most common treatment
modality. There was not a significant difference in outcome based on treatment; however, surgery
and chemotherapy were associated with death from a cause other than their tumor.
Animals 2022,12, 258. https://doi.org/10.3390/ani12030258 https://www.mdpi.com/journal/animals

Animals 2022,12, 258 2 of 17
Keywords: Boidae; chemotherapy; Colubridae; neoplasia; oncology; surgery; prevalence; Viperida
1. Introduction
Research involving neoplasia in snakes is not new and in fact has occurred over nu-
merous years involving evaluations of medical cases at the London Zoo, the Registry of
Tumors of Lower Animals [
1
–
3
], and individual laboratories or facilities [
4
–
6
]. Overall,
these previous studies have found that neoplasia appears to be common in snakes [
7
,
8
],
and it is well shown in the literature that snakes tend to have higher prevalence of cancer
reported than other reptiles [
7
,
9
]. However, these publications on snake neoplasia have typ-
ically focused only on the types of neoplasia diagnosed [
10
,
11
], the prevalence of neoplasia
at a single institution or laboratory [
4
,
12
], or on an individual animal’s treatment [
13
,
14
]. A
type of multi-institutional study on museum specimens has been done as well as a literature
review, however, this study was never able to confirm the presence of neoplasia due to the
lack of confirmatory testing [
15
]. Other studies do exist on reporting snake neoplasia preva-
lence within a group of snakes, including cutaneous chromatophoromas [
11
,
16
–
19
]. One of
these previous publications evaluated the prevalence of neoplasia from cases submitted
to a diagnostic laboratory and they found that the prevalence was highest in Crotalids,
Viperids, and Boids [
7
]. This study, however, only looked at the samples submitted to their
laboratory and was unable to evaluate the prevalence based on the populations of animals
from where they originated. Additionally, previous studies found that malignant tumors
are most commonly reported in snakes, and that they were mesenchymal or epidermal in
origin [4,6,7,20].
Previous published literature also is lacking on evaluation of treatments and survival
times. Although papers exist on treatments in individual snakes, as well as a report on
treatment of other snakes, there is no mention of overall survival time [
13
,
21
,
22
]. Currently,
even though snake metabolism is very different from mammal metabolism, current predic-
tions of a snake’s survival with neoplasia are based on survival time in domestic dogs and
cats with cancer due to a lack of survival studies in snakes.
The present study therefore focused on (a) investigating the prevalence of neoplasia
for snakes housed at six institutions using the combined total population for each snake
species at these institutions, and (b) determining if a snake with neoplasia was more likely
to die or be euthanized due to neoplasia versus another cause in order to evaluate survival
for snakes with neoplasia.
2. Materials and Methods
2.1. Case Selection
Six institutions participated in this study. Complete medical records were obtained for
snakes that had a biopsy or necropsy report with a histologic diagnosis of neoplasia. Cases
were confirmed to be neoplasia by board-certified veterinary pathologists working at either
independent laboratories or university settings. Cases were confirmed to be neoplasia
based on the diagnosis in the medical record and classified as to current nomenclature by
board-certified veterinary pathologists specializing in zoological medicine cases (Troan,
Garner). To determine prevalence for each species, the total number of individuals of that
species housed at each institution for a given time were gathered from their respective
medical record managers or by obtaining species totals from the Species360 Zoological
Information Management System (ZIMS). Population totals included all ages and several
snakes that were lost to follow-up or that were transferred to other institutions.
2.2. Medical Records Review
Medical records of the six participating institutions were reviewed. Animals were
categorized taxonomically (family and species), by sex (male, female, unknown), and by
maturity (adult; juvenile being <3 months of age; or unknown). Diagnoses were grouped by

Animals 2022,12, 258 3 of 17
primary histologic diagnosis and behavior (benign versus malignant). All lymphomas or
leukemias were designated as malignant due to the multicentric nature of these neoplasms.
Animals that had detectable metastases were categorized in the metastasis category. Treat-
ments were separated into general groups including (1) surgery only, (2) chemotherapy
(which included steroid therapies and non-steroidal anti-inflammatory drugs (NSAIDs)
used longer than 5 days for postoperative analgesia), (3) surgery and chemotherapy (in-
cluding steroid and nonsteroidal therapies (as above)), (4) supportive care (which in-
cluded systemic or topical antibiotics and NSAIDs (as above)), (5) unknown treatment, and
(6) no treatment provided. Medical records were collected and managed using RED-
Cap electronic data capture tools hosted at North Carolina State University College of
Veterinary Medicine [
23
,
24
]. REDCap (Research Electronic Data Capture, Vanderbilt Uni-
versity, Nashville, TN, USA) is a secure, web-based software platform designed to support
data capture for research studies, providing (1) an intuitive interface for validated data
capture; (2) audit trails for tracking data manipulation and export procedures; (3) auto-
mated export procedures for seamless data downloads to common statistical packages; and
(4) procedures for data integration and interoperability with external sources.
2.3. Data Analysis
Database information was analyzed using IBM Corp. Released 2019. IBM SPSS
Statistics for Windows, Version 26.0. Armonk, NY, USA [
25
] and R statistical computing
software (version 3.6.1; R Core Team 2020. R: A language and environment for statistical
computing. R foundation for Statistical Computing, Vienna, Austria, https://www.R-
project.org/ accessed 18 January 2022) [
26
]. Prevalence of neoplasia per species was done
for those that have greater than 10 total individuals (those with neoplasia and without).
Frequencies, survival curve analysis, and boosting analyses were used to evaluate the
data. For survival curve analysis, Kaplan–Meier survival curves and log-rank tests were
generated with the survminer package (R package version 0.4.1, https://CRAN.R-project.
org/package=survminer accessed on 18 January 2022) [
27
] and survival package (R package
version 2.38, https://CRAN.R-project.org/package=survival accessed 18 January 2022) [
28
].
For the statistical method of boosting, the mboost package (Model-based boosting, R
package version 2.6.0, https://CRAN.R-project.org/package=mboost accessed 18 January
2022) [
29
] was used. Neoplasms were grouped into more general classification categories
by behavior (benign vs. malignant) as well as by tissue and tumor type for mboost
evaluation of survival of animals affected with these types of neoplasms. For boosting
analysis, predictor variables were modeled with the use of btree as a base-learner for
decision stumps. The set of eight predictor variables were presence or lack of detectable
of metastasis, primary histological diagnosis, type of tumor, number of observed tumor
types (1 or 2), type of treatment, taxonomic family, species, and sex. Outcomes were
assigned to snakes, with “+1” designated for those that died or were euthanized due to
the neoplasm and “0” designated for those that were euthanized due to another cause.
Snakes without a known cause of death, or who were lost to follow-up, were excluded
from outcome analysis. The modeled effects of the eight predictor variables with outcomes
for each animal evaluated were compared to a set of 2000 null model distributions of
effects generated from modeling done with permutated outcomes, with p< 0.05 being
the threshold of significance regarding the tails of the null model distribution (two-sided
hypothesis), similar in method to Mayr et al. [
30
]. Prevalence was calculated only for
species with 10 or more individuals in the study population.
3. Results
3.1. Study Population
A total of 133 snake neoplasia cases representing 65 different species were included.
Time spans varied by institution due to medical record accessibility. Time spans were
Institution 1: (1985–2018); Institution 2: (2013–2017); Institution 3: (2003–2018); Institution
4: (1974–2018); Institution 5: (1980–2018); and Institution 6: (2002–2018). Participating

Animals 2022,12, 258 4 of 17
institutions are located in Colorado, Ohio, North Carolina, and Texas (alphabetical order,
see acknowledgements).
3.2. Neoplasia Information
There were 149 neoplasms included in the study. Malignant tumors predominated
(86.6%, n= 129 of 149). Only 13 benign tumors were identified (8.7%, n= 13 of 149), and
there were 7 unspecified tumors (4.7%, n= 7 of 149) as their behavior was not definitive
based on histology. The sex distribution consisted of 67 females, 63 males, and 3 of
undetermined sex. Of those with benign neoplasia 4 were females and 5 were males.
There were 61 females and 56 males with malignant neoplasia and 2 females and 2 males
with unspecified benign or malignant neoplasia. The median age at the time of diagnosis
was 138 months, and ages ranged from 42–420 months. The average age of animals with
benign neoplasms was
176 months
(median 141 months) and the average age of those with
malignant neoplasms was 150 months (132 median). Seven individuals were of unknown
age. Detectable metastasis was reported in 42.9% (n= 57 of 133) of snakes with neoplasia.
Multi-organ involvement existed in 27 snakes, while 17 snakes had multicentric lymphoma
or leukemia (Table 1).
Table 1. Tumor Type and Prevalence by Species.
Family Species and
Prevalence Common Name Benign Malignant Unspecified
Boidae
Acrantophis
dumerili
2.4% (1/41)
Dumeril’s Ground
Boa
(1) Soft Tissue Sarcoma
Boa constrictor
14.3% (2/14) Boa Constrictor
(1) Neuroendocrine
Tumor
(1) Soft Tissue Sarcoma
Chilabothrus granti
7.7% (1/13) Virgin Islands Boa
(1) Thyroid Carcinoma
(1) Hepatocellular
Carcinoma
Eunectes murinus
4.3% (1/23) Green Anaconda (1) Sertoli Cell
Tumor
Lichanura trivirgata
15.8% (3/19) Rosy Boa (1) Pancreatic
Adenoma
(1) Undifferentiated
Carcinoma
(1) Histiocytic Sarcoma
Sanzinia
madagascariensis
20.0% (1/5)
Madagascar Tree
Boa
(1) Soft Tissue Sarcoma
Colubridae
Coelognathus
radiatus
4% (4/101)
Radiated Ratsnake
(2) Hepatocellular
Carcinoma
(1) Lym-
phoma/Leukemia
(1) Renal
Adenocarcinoma
Elaphe taeniura
11.1% (1/9)
Taiwan Beauty
Snake
(1) Soft Tissue Sarcoma
Heterodon nasicus
10.3% (3/29)
Western
Hog-Nosed Snake
(2) Hepatocellular
Carcinoma
(1) Soft Tissue Sarcoma
Heterodon
platirhinos
25.0% (2/8)
Eastern
Hog-Nosed Snake
(1) Soft Tissue Sarcoma
(1) Malignant
Chromatophoroma
(unspecified)

Animals 2022,12, 258 5 of 17
Table 1. Cont.
Family Species and
Prevalence Common Name Benign Malignant Unspecified
Lampropeltis getula
17.9% (5/28) Kingsnake (1) Renal
Adenoma
(3) Soft Tissue Sarcoma
(1) Renal Carcinoma
(1) Hepatic
Adenocarcinoma
(1) Chro-
matophoroma
(iridophoroma)
Lampropeltis
triangulum
1.8% (1/56)
Eastern Milksnake (1) Gastrointestinal
Adencocarcinoma
Leioheterodon
madagascariensis
1.3% (1/78)
Madagascar Giant
Hognose Snake (1) Osteosarcoma
Nerodia sipedon
30.8% (4/13)
Common Or
Northern
Watersnake
(3) Soft Tissue Sarcoma
(1) Malignant
Chromatophoroma
(iridophoroma)
(1) Malignant
Chromatophoroma
(Uncharacterized)
Oreocryptophis
porphyraceus
5.3% (1/19)
Black-Banded
Trinket Snake
(1) Hepatocellular
Carcinoma
Pantherophis
guttatus
9.6% (11/115)
Corn snake
(1) Granulosa Cell
Tumor
(1) Lym-
phoma/Leukemia
(7) Soft Tissue Sarcoma
(1) Osteosarcoma
(2) Hemangiosarcoma
Pantherophis
obsoletus (Or)
alleghaniensis
7.4% (14/189)
Ratsnake
(5) Soft Tissue Sarcoma
(1) Gastrointestinal
Adencocarcinoma
(1) Renal Carcinoma
(1) Chondrosarcoma
(4)
Lymphoma/leukemia
(1) Osteosarcoma
(1) Granulosa Cell
Tumor
Pituophis catenifer
5.4% (2/37)
Gophersnake
(or) Bullsnake
(2) Hepatobiliary
Carcinoma
Pituophis
lineaticollis
25.0% (1/4)
Middle American
Gophersnake
(1) Undifferentiated
Carcinoma
Pituophis ruthveni
2.4% (1/42)
Louisiana
Pinesnake
(1) Soft Tissue Sarcoma
Rhamphiophis
oxyrhynchus
14.3% (1/7)
Rufous-Beaked
Snake
(1) Neuroendocrine
Tumor
Rhinocheilus lecontei
16.7% (1/6)
Long-Nosed Snake
(1) Gastrointestinal
Adencocarcinoma
Rhynchophis
boulengeri
5.3% (1/19)
Rhinoceros Snake (1) Lym-
phoma/Leukemia
Salvadora bairdi
4.8% (1/21)
Baird’s Patchnose
Snake
(1) Renal
Adenocarcinoma

Animals 2022,12, 258 6 of 17
Table 1. Cont.
Family Species and
Prevalence Common Name Benign Malignant Unspecified
Thamnophis
cyrtopsis
100.0% (1/1)
Black-Necked
Gartersnake
(1) Malignant
Chromatophoroma
(Melanoma)
Thamnophis exsul
10.5% (2/19)
Exiled Gartersnake
(2) Biliary
Cystadenoma
Thamnophis radix
(4)
0.8% (4/500)
Plains Gartersnake
(1) Malignant
Chromatophoroma
(Melanoma)
(1) Granulosa Cell
Tumor
(1) Undifferentiated
Carcinoma
(1) Hepatocellular
Carcinoma
Thamnophis sirtalis
100.0% (1/1)
Common
Gartersnake
(1) Biliary
Cystadenoma
(1) Squamous Cell
Carcinoma
Trimorphodon
lambda
25.0% (1/4)
Sonoran Lyresnake
(1) Renal Carcinoma
Elapidae
Hemachatus
haemachatus
14.3% (2/14)
Ringhals Cobra
(1) Lym-
phoma/Leukemia
(1) Gastrointestinal
Adencocarcinoma
Hydrodynastes gigas
1.4% (1/72) False Water Cobra
(1) Renal
Adenocarcinoma
(1) Pancreatic
Adenocarcinoma
Naja pallida
3.8% (1/26)
Red Spitting Cobra
(1) Renal
Adenocarcinoma
Ophiophagus
hannah
15.4% (2/13)
King Cobra (1) Granulosa
Cell Tumor
(1) Lym-
phoma/Leukemia
(1) Undifferentiated
Adenocarcinoma
Pythonidae Antaresia childreni
2.3% (1/44) Children’s Python
(1) Lym-
phoma/Leukemia
(1) Soft Tissue Sarcoma
Liasis mackloti
50.0% (1/2) Macklot’s Python (1) Lym-
phoma/Leukemia
Malayopython
reticulatus
25.0% (1/4)
Reticulated Python
(1) Hepatocellular
Carcinoma
Morelia spilota
12.5% (1/8) Carpet Python (1)Esophageal
Carcinoma
Morelia viridis
1.7% (1/59) Green Tree Python (1) Squamous Cell
Carcinoma
Python bivittatus
12.5% (1/8) Burmese Python
(1) Soft Tissue Sarcoma
Python regius
10.5% (2/19) Ball Python
(1) Squamous Cell
Carcinoma
(1) Gastrointestinal
Adenocarcinoma
(1) Chro-
matophoroma
(melanophoroma)

Animals 2022,12, 258 7 of 17
Table 1. Cont.
Family Species and
Prevalence Common Name Benign Malignant Unspecified
Viperidae
Agkistrodon
contortrix
37.5% (3/8)
Copperhead
(2)
Hepatocellular
Adenoma
(1) Lym-
phoma/Leukemia
Agkistrodon
piscivorus
18.2% (2/11)
Cottonmouth
(1) Soft Tissue Sarcoma
(1) Lym-
phoma/Leukemia
Atheris squamigera
7.4% (2/27)
African Bush Viper
(1) Hepatic
Cystadenocarcinoma
(1) Oviduct
Adenocarcinoma
Bitis arietans
50.0% (2/4) Puff Adder (1) Renal Carcinoma
(1) Soft Tissue Sarcoma
Bitis nasicornis
5.9% (3/51) Rhinoceros Viper
(1) Renal
Adenocarcinoma
(1) Cholangiocellular
carcinoma
(1) Renal Carcinoma
(1) Lym-
phoma/Leukemia
Bothriechis rowleyi
4.2% (2/48)
Rowley’s Palm Pit
Viper
(1) Soft Tissue Sarcoma
(1) Squamous Cell
Carcinoma
Bothriechis schlegelii
4.4% (2/45) Eyelash Viper
(2) Soft Tissue Sarcoma
Bothrops asper
2.4% (1/41) Terciopelo (1) Renal
Cystadenoma
(1) Soft Tissue Sarcoma
Crotalus adamanteus
26.3% (5/19)
Eastern
Diamond-Backed
Rattlesnake
(2) Soft Tissue Sarcoma
(1) Lym-
phoma/Leukemia
(1) Squamous Cell
Carcinoma
(1) Hemangiosarcoma
(1) Sertoli Cell
Tumor
Crotalus atrox
9.5% (2/21)
Western
Diamond-Backed
Rattlesnake
(1) Renal
Adenocarcinoma
(1) Cholangiocellular
Carcinoma
(1) Sertoli Cell
Tumor
Crotalus cerastes
20.0% (1/5) Sidewinder (1) Hepatic
Adenoma
(1) Chro-
matophoroma
(Melanophoroma)
Crotalus culminatus
3.6% (2/55)
Northwestern
Neotropical
Rattlesnake
(1) Soft Tissue Sarcoma
(1) Biliary
Adenocarcinoma
Crotalus horridus
22.7% (5/22)
Timber Rattlesnake
(1) Lipoma
(3) Soft Tissue Sarcoma
(1) Ovarian Carcinoma
Crotalus lepidus
14.3% (1/7) Rock Rattlesnake (1) Hepatic
Adenoma
(1) Malignant
Chromatophoroma
(Melanophoroma)
Crotalus molossus
20.0% (1/5)
Black-Tailed
Rattlesnake
(1) Soft Tissue Sarcoma
(1) Hepatocellular
Carcinoma

Animals 2022,12, 258 8 of 17
Table 1. Cont.
Family Species and
Prevalence Common Name Benign Malignant Unspecified
Crotalus viridis
20.0% (1/5) Prairie Rattlesnake
(1) Hepatocellular
Carcinoma
(1) Soft Tissue Sarcoma
Lachesis muta
15.4% (2/13)
South American
Bushmaster
(2) Hepatocellular
Carcinoma
Montivipera raddei
7.7% (1/13) Armenian Viper (1) Pancreatic
Carcinoma
Protobothrops
flavoviridis
16.7% (1/6)
Habu
(1) Soft Tissue Sarcoma
Sistrurus catenatus
25.0% (1/4)
Eastern
Massasauga (1) Osteosarcoma
Sistrurus miliarius
14.3% (2/14)
Pygmy Rattlesnake
(1) Pancreatic
Adenoma
(1) Biliary
Adenocarcinoma
Trimeresurus
flavomaculatus
10.0% (1/10)
Philippine Pit
Viper
(1) Lym-
phoma/Leukemia
Trimeresurus
mcgregori
2.3% (1/44)
McGregor’s Tree
Viper
(1) Soft Tissue Sarcoma
Trimeresurus
sumatranus
1.4% (1/74)
Sumatran Pit Viper
(1) Lym-
phoma/Leukemia
Vipera
transcaucasiana
5.3% (1/19)
Transcaucasian
Long-Nosed Viper
(1) Soft Tissue Sarcoma
3.3. Neoplasia Prevalence
The neoplasia prevalence by taxonomic family (including only those species with 10
or more individuals) ranged from 3.3–7.3% and was not significantly different (
χ2
= 1.88,
p= 0.17) among the various families.
The highest prevalence of neoplasia by species, was in the common or northern wa-
tersnake (Nerodia sipedon) (30.8%, n= 4 of 13) followed by the eastern diamond-backed rat-
tlesnake (Crotalus adamanteus) (26.3%, n= 5 of 19) and the timber rattlesnake
(Crotalus horridus)
(22.7%, n= 5 of 22) (Table 1). The species with the lowest prevalence was the plains
gartersnake (Thamnophis radix) (0.8%, n= 4 of 500). Both, the species with the highest
neoplasia prevalence (the watersnake) and the species with the lowest prevalence (the
plains gartersnake) were from the Colubridae family of snakes. The prevalence of neoplasia
was significantly different between these two species, (
χ2
= 74.13, p< 0.01). Prevalence of
neoplasia and total number of snakes per institution are listed in Table 2.
3.4. Treatment
Treatment for neoplasia was administered to 27.1% (n= 36 of 133) of the snakes. Of the
36 snakes that were treated, a survival time was reported in all but three snakes which were
euthanized during surgery (Table 3includes the 33 snakes that reported a survival time).
The median survival time was 5.5 months (range 0.25–108 months). The main treatment
modality used was surgery (complete or incomplete excision) (97.2%, 35 of 36). Surgery in
combination with chemotherapy was employed in three snakes, and surgery and radiation
were performed in two snakes. Surgery, chemotherapy, and radiation were all used to treat
one snake, and chemotherapy alone was used to treat one snake. Supportive care in the

Animals 2022,12, 258 9 of 17
form of antibiotics, fluids, or NSAIDs was used in eight snakes in addition to a treatment
modality and used in four snakes without other treatment modalities (Table 3).
Table 2. Prevalence of neoplasia at each participating institution.
Institution Total Snakes
with Neoplasia
Total Number
of Snakes of
Affected
Species
Number of
Different
Affected
Species
Prevalence
1 32 162 20 19.8%
2 10 72 4 13.9%
3 16 77 9 20.8%
4 19 250 14 7.6%
5 31 651 26 4.8%
6 25 1049 16 2.4%
Table 3. Treatment and Survival.
Family Common Name/Scientific
Name Tumor (s) Survival in
Months
Treatment ±
Supportive Care
Boidae
Boa constrictor
Boa constrictor Benign carcinoid tumor 0.25 none
Boa constrictor
Boa constrictor Soft tissue sarcoma 1 surgical excision only
Rosy boa
Lichanura trivirgata Histiocytic sarcoma 7 surgical excision only
Madagascar tree boa
Sanzinia madagascariensis Soft tissue sarcoma 22 surgical excision only
Colubridae
Western hog-nosed snake
Heterodon nasicus Hepatocellular carcinoma 10 none
Western hog-nosed snake
Heterodon nasicus Soft tissue sarcoma 6 surgical excision *
Eastern hog-nosed snake
Heterodon platirhinos Soft tissue sarcoma 15.5 none
Kingsnake
Lampropeltis getula
Soft tissue sarcoma,
Hepatocellular
adenocarcinoma
10.5 none
Kingsnake
Lampropeltis getula
Soft tissue sarcoma,
Chromatophoroma
(uncharacterized)
8 surgical excision only
Common or northern
watersnake
Nerodia sipedon
Soft tissue sarcoma,
Malignant chromatophoroma 5 surgical excision *
Common or northern
watersnake
Nerodia sipedon
Malignant chromatophoroma 1 surgical excision only
Common or northern
watersnake
Nerodia sipedon
Soft tissue sarcoma 0.5 surgical excision only
Corn snake
Pantherophis guttatus Soft tissue sarcoma 2 none

Animals 2022,12, 258 10 of 17
Table 3. Cont.
Family Common Name/Scientific
Name Tumor (s) Survival in
Months
Treatment ±
Supportive Care
Corn snake
Pantherophis guttatus Soft tissue sarcoma 12
surgical excision and
radiation and
chemotherapy
(Piroxicam) *
Corn snake
Pantherophis guttatus Hemangiosarcoma 2 surgical excision only
Corn snake
Pantherophis guttatus Soft tissue sarcoma 108 surgical excision only *
Corn snake
Pantherophis guttatus Soft tissue sarcoma 18 surgical excision and
radiation
Corn snake
Pantherophis guttatus Soft tissue sarcoma 5.5
surgical excision and
chemotherapy
(Cyclophosphamide
and Piroxicam)
Ratsnake
Pantherophis obsoletus or
alleghaniensis
Colonic adenocarcinoma 7 surgical excision only *
Ratsnake
Pantherophis obsoletus or
alleghaniensis
Chondrosarcoma 15 none
Ratsnake
Pantherophis obsoletus or
alleghaniensis
Leukemia 1 none
Ratsnake
Pantherophis obsoletus or
alleghaniensis
Osteosarcoma 6 supportive care only *
Ratsnake
Pantherophis obsoletus or
alleghaniensis
Soft tissue sarcoma 4 surgical excision only
Gophersnake(or) Bullsnake
Pituophis catenifer Hepatocellular carcinoma 1 none
Black-necked gartersnake
Thamnophis cyrtopsis Malignant chromatophoroma 5.5 surgical excision only
Plains gartersnake
Thamnophis radix Malignant chromatophoroma 13 surgical excision and
radiation
Plains gartersnake
Thamnophis radix
Malignant granulosa cell
tumor 1 surgical excision only
Common gartersnake
Thamnophis sirtali Squamous cell carcinoma 9 not known
Elapidae
Ringhals cobra
Hemachatus haemachatus Lymphoma 0.75 none
False water cobra
Hydrodynastes gigas
Renal and Pancreatic
adenocarcinoma 71 surgical excision only
Red spitting cobra
Naja pallida
Renal
carcinoma/adenocarcinoma 35 surgical excision only
King cobra
Ophiophagus hannah Lymphoma 11 chemotherapy only
(Lomustine)

Animals 2022,12, 258 11 of 17
Table 3. Cont.
Family Common Name/Scientific
Name Tumor (s) Survival in
Months
Treatment ±
Supportive Care
Pythonidae
Children’s python
Antaresia childreni
Lymphoma,
Soft tissue sarcoma 3 surgical excision only
Carpet python
Morelia spilota Esophageal carcinoma 2.5 surgical excision only
Green tree python
Morelia viridis Squamous cell carcinoma 7 not known
Burmese python
Python bivittatus Soft tissue sarcoma 1 surgical excision only
Ball python
Python regius Squamous cell carcinoma 84
surgical excision and
chemotherapy
(Carboplatin) *
Viperidae
Cottonmouth
Agkistrodon piscivorus Soft tissue sarcoma 0.25 surgical excision only
Eyelash viper
Bothriechis schlegelii Soft tissue sarcoma 16 surgical excision only
Eyelash viper
Bothriechis schlegelii Soft tissue sarcoma 5 none
Eastern diamond-backed
rattlesnake
Crotalus adamanteus
Lymphoma 20
surgical excision and
chemotherapy
(Cyclophosphamide)
Eastern diamond-backed
rattlesnake
Crotalus adamanteus
Squamous cell carcinoma 18.5 surgical excision only
Eastern diamond-backed
rattlesnake
Crotalus adamanteus
Hemangiosarcoma,
Sertoli cell tumor
(uncharacterized)
7 surgical excision only
Sidewinder
Crotalus cerastes
Chromatophoroma
(uncharacterized),
Hepatobiliary adenoma
1 none
Timber rattlesnake
Crotalus horridus Ovarian carcinoma 0.25 none
Timber rattlesnake
Crotalus horridus Soft tissue sarcoma 0.25 none
Timber rattlesnake
Crotalus horridus Soft tissue sarcoma 1 surgical excision only
Timber rattlesnake
Crotalus horridus Lipoma 24 surgical excision only
Rock rattlesnake
Crotalus lepidus
Malignant chromatophoroma,
Hepatobiliary adenoma 1 none
Prairie rattlesnake
Crotalus viridis
Hepatocellular carcinoma,
Soft tissue sarcoma 1 none
South american bushmaster
Lachesis muta
Hepatocellular
carcinoma/adenocarcinoma 3 none
Eastern massasauga
Sistrurus catenatus Osteosarcoma 3.5 surgical excision *
Sumatran pit viper
Trimeresurus sumatranus Lymphoma 0.36 none
* A nonsteroidal anti-inflammatory (NSAID) was also used less than 5 days for pain control.

Animals 2022,12, 258 12 of 17
3.5. Outcome and Survival
Outcome effects and significance of predictors were estimated and evaluated through
boosting and permutation as described, with the outcome effects representing estimates of
coefficients in a generalized linear model for death due to tumor, or death due to another
cause. Animals with malignant neoplasms were significantly more likely to die of their
cancer (p< 0.05) and snakes with benign neoplasms were significantly less likely to die
of their cancer (a cause of death other than tumor) (p< 0.5). Chromatophoromas were
identified as a neoplasm significantly associated with a cause of death other than tumor
(p< 0.05). Snakes without metastases were also significantly associated with a non-tumor-
related cause of death (p< 0.05). Snakes with metastases or an unknown condition of
metastasis were significantly associated with a tumor-related cause of death (p< 0.05).
Number of unique tumors, species and sex were not significantly associated with a cause
of death due to neoplastic disease and had absolute values of outcome effect <0.01, with
the exception of the Thamnophis radix species having an outcome effect of 0.014. Significant
outcome effects for predictor variable values are shown in Table 4.
Table 4.
Predictor variable values of snakes that had a significant association with tumor versus
non-tumor causes of death based on boosting and comparing each variable’s modeled outcome effect
to null model distribution of effects generated from modeling done with permutated cause of death
outcomes (p< 0.05).
Predictor Variable Predictor Variable Value Sample Size aOutcome Effect b
Type of Neoplasm Malignant 112 0.71
Type of Neoplasm Benign 9 −0.71
Metastasis (Yes/No) Yes 56 0.060
Metastasis (Yes/No) Unknown Metastasis 2 0.060
Metastasis (Yes/No) No 63 −0.055
Tumor Type Chromatophoroma 4 −0.20
a
This is a subset of clinical case counts for which there were specific values reported across the set of eight
predictor variables with a determined outcome of death due to tumor or death due to another cause. In the case
of multiple tumor types and status of being malignant or benign, the tally and modeling is based on random
sampling of a tumor type and its associated status for each clinical case.
b
Outcome effects are relative to death
due to tumor or death due to another cause with each clinical case scored as +1 and 0 respectively.
Cases for other modalities other than surgery were too low to analyze separately, there-
fore cases treated with multiple modalities (surgery, chemotherapy, and/or radiation) were
grouped. Median survival times for no treatment, surgery only, and multiple modalities
were 1, 5.5, and 13 months respectively. Survival curves plotted for those snakes that were
treated and those that were not, were not significantly different based on a log-rank test
(p= 0.3) (Figures 1and 2).

Animals 2022,12, 258 13 of 17
Animals 2022, 12, x 13 of 17
Cases for other modalities other than surgery were too low to analyze separately,
therefore cases treated with multiple modalities (surgery, chemotherapy, and/or radia-
tion) were grouped. Median survival times for no treatment, surgery only, and multiple
modalities were 1, 5.5, and 13 months respectively. Survival curves plotted for those
snakes that were treated and those that were not, were not significantly different based
on a log-rank test (p = 0.3) (Figures 1 and 2).
Figure 1. Overall survival curve of snakes treated for their neoplasia.
Figure 1. Overall survival curve of snakes treated for their neoplasia.
Animals 2022, 12, x 13 of 17
Cases for other modalities other than surgery were too low to analyze separately,
therefore cases treated with multiple modalities (surgery, chemotherapy, and/or radia-
tion) were grouped. Median survival times for no treatment, surgery only, and multiple
modalities were 1, 5.5, and 13 months respectively. Survival curves plotted for those
snakes that were treated and those that were not, were not significantly different based
on a log-rank test (p = 0.3) (Figures 1 and 2).
Figure 1. Overall survival curve of snakes treated for their neoplasia.
Figure 2. Overall survival curve of snakes not treated for their neoplasia.
4. Discussion
By collecting data from multiple institutions, this study reaffirmed that snakes have a
tendency to develop malignant neoplasia indicating that histological sampling of masses
may be key to early diagnosis and more successful treatment. Additionally, this study
calculated species specific prevalence for 65 species and specifically for 44 species in which

Animals 2022,12, 258 14 of 17
more than 10 individuals were included which were used to calculate overall family
prevalence. The reason to only calculate prevalence for 10 or more individuals was to
reduce the potential for inaccurate levels of prevalence to be reported for those species
having low numbers of animals. Although this study evaluated neoplasia in 65 species, we
were not able to evaluate the prevalence of neoplasia in all snakes due to which species
were present at the six institutions evaluated. Therefore, results of this study can only be
applied to those that were evaluated and included in this study. It is possible that a potential
variation in necropsy techniques or time of death prior to sampling could have impacted
the ability to diagnose neoplasia at certain facilities, but we attempted to minimize this
through involving multiple facilities. Finally, snakes that received no treatment had lower
survival times than those that were treated. This may have been because some snakes
showed advanced disease at the time of first diagnosis and therefore were not considered
suitable candidates for treatment, or those snakes may have been diagnosed at the time of
death due to their cancer and as such would make their survival times lower.
By including both neoplasia cases rising to the level of treatment along with the
non-affected population, the inclusion of the latter category by this study has helped
address publication bias that has been oriented toward the former. This, further addresses
laboratory submission bias as published reports and submitted cases preferentially include
cases that are interesting, unique, or survive due to a certain therapy. We also avoided
regional bias by including cases from multiple institutions across the United States. This
collection of cases from multiple areas also helps to minimize a genetic component. More
charismatic, larger or more colorful snakes can sometimes be chosen to be exhibited, which
can skew the number of individuals representing a given species of snakes. This bias
was likely reduced by using multiple institutions in different areas with different-sized
facilities that, together, are less likely to ascribe to any singular modality for choosing a
snake species.
The present study documented that the most prevalent neoplasms in snakes were
malignant mesenchymal tumors of the skin and soft tissue (n= 45 of 149), malignant
tumors of the alimentary system/liver/gallbladder (n= 31 of 149), malignant tumors of
mast cell/hemolymphatic/histocytic origin (n= 18 of 149), and malignant tumors of the
urinary/genital systems (n= 15 of 149).
We did not find any statistically significant difference in prevalence between families.
There was a statistically significant difference in prevalence by species.
We did not find any differences in prognostic outcome between families or genera.
These families and genera typically range in size and length. There could potentially be a
bias introduced that with smaller or skinnier snakes it may be easier to observe neoplasia
than with larger or wider diameter snakes, but as the length and width of the snakes was
not routinely recorded in the medical records, it was not able to be evaluated.
It is not surprising that those animals with malignant, metastatic, or indeterminant
metastatic neoplasia were more likely to die from the tumor than those with benign or
non-metastatic neoplasms. Malignant and metastatic neoplasms tend to negatively affect
multiple organ systems, which explains the negative outcome. The only neoplasm that did
not contribute significantly to the death of the animal in our data was a chromatophoroma,
which is different from previously published literature [16].
Treatment was not commonly performed in the snakes that we evaluated, possibly
because very early clinical signs of neoplasia may be limited to subtle changes in behavior
or physical appearance which may be difficult to detect during routine husbandry ob-
servations. These behavioral cues can include, but are not limited to, changes in feeding
behavior, odd body positioning, and increases or decreases in activity [
31
,
32
]. External
physical changes often are dermal abnormalities such as frequent and/or incomplete ecd-
ysis, areas of discoloration or infection, cutaneous or intracoelomic swellings, or weight
changes inconsistent with body condition [
21
]. Finally, clinical signs may not be observable
until widespread (metastatic) or advanced disease. With continued, improved frequency
of physical examinations in zoological facilities as well as in those kept as pets and with

Animals 2022,12, 258 15 of 17
continued use of diagnostic imaging such as ultrasound, radiographs, and computed to-
mography (CT) scans, this could aid in diagnosing these neoplasias at an earlier stage
prior to metastasis and may allow for additional diagnostics such as fine needle aspirates,
biopsies, or surgical removal of masses.
Consistent with previous reports, surgical excision was the most common treatment
modality and showed an increase in survival time in certain cases [
13
,
33
]. Additionally, a
previous study found that even removing a portion of a neoplastic mass had a positive
effect on survival, which appeared to be similar to results in this study [
34
]. Specifically,
a cornsnake with a surgically removed soft tissue sarcoma without metastasis had the
longest survival time of 108 months compared to other snakes that received some form
of treatment specifically for their neoplasia. In general, the only other therapies that had
a survival time of greater than 22 months were surgical or surgery and chemotherapy
treatments (survival time 84 months). This survival time exceeds that of two other snakes
treated with chemotherapy and surgery (5.5 and 20 months) as well as snakes treated with
chemotherapy only (11 months) or surgery, chemotherapy, and radiation (12 months). Prior
reports of published case reports on radiation and chemotherapy treatments in snakes,
documents an increase in survival time for some patients when treated with radiation and
chemotherapy as sole treatment therapies, or when used in combination with surgery [
3
,
35
].
It must be noted, however, that longer survival times may not necessarily correlate with
improved quality of life due to potential side effects of chemotherapy and radiation. Many
medical or radiation treatment protocols were extrapolated from domestic animal dosages
and frequency schedules, which may not be appropriate for snakes and could account
for the lower survival times. Overall, no treatment method demonstrated a statistically
significant improvement in prognosis, but this may be due to the low number of treated
animals in this study or to the treatment protocols not being tailored to snakes or their
neoplasia type. As more frequent examinations occur and diagnostic techniques improve,
more cases will be diagnosed and potentially treated, thereby improving our knowledge
about neoplastic disease, treatment, and survival in these species.
5. Conclusions
Our data show that snakes have a moderate risk of developing neoplasia, but when
they do, it is likely malignant. Surgical excision patients survive longer than patients that
received no treatment. Modalities such as chemotherapy and radiation need further refine-
ment to result in prolonged survival times compared to surgical removal only. However,
relatively few cases of snakes with cancer were treated in this study. Although data and
results collected for this study represent multiple institutions and reduce bias, furthering
knowledge of neoplasia prevalence, behavior, and treatment in snakes will benefit from a
larger aggregated dataset (www.escra.org (accessed on 18 January 2022)), in particular a
larger number of treated cases.
Author Contributions:
Conceptualization, T.M.H., E.G.D.; validation, B.V.T.; formal analysis, S.H.H.;
data curation, E.G.D., M.S., M.M.G.; writing—original draft preparation, E.G.D., T.M.H., A.M., B.V.T.,
M.S., S.S.; writing—E.G.D., T.M.H., A.M., B.V.T., S.H.H., T.T., M.M.G.; supervision, T.M.H.; project
administration, T.M.H., E.G.D. All authors have read and agreed to the published version of the
manuscript.
Funding:
This research was funded by the National Institutes of Health, grant number U54 CA217376.
Institutional Review Board Statement:
This study was conducted in approval of North Carolina
State University’s Institutional Animal Care and Use Committee 21-117.
Informed Consent Statement: Not applicable due to this study consisting of animal patients.
Data Availability Statement:
Deidentified data are available through an approved research request to
the Exotic Species Cancer Research Alliance (https://escra.cvm.ncsu.edu/ (accessed on 18 January 2022)).

Animals 2022,12, 258 16 of 17
Acknowledgments:
The authors thank the following staff for help with gathering data from the
zoos’ record systems: Emily Christiansen and Heather Broadhurst (VT) (North Carolina Aquariums),
Randy Junge (Columbus Zoo and Aquarium), Larry “Jb” Minter (North Carolina Zoo), Rob Coke
(San Antonio Zoo), and Jessica Grote (Denver Zoo).
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Harshbarger, J.C. Registry of Tumors in Lower Animals; Activities Report Supplement (1974–1977); Museum of Natural History,
Smithsonian Institution: Washington, DC, USA. Available online: https://library.si.edu/digital-library/book/activitiesrep19741
977regi (accessed on 23 November 2021).
2.
Harshbarger, J.C. Registry of Tumors in Lower Animals; Activities Report Supplement (1978–1981); Museum of Natural History,
Smithsonian Institution: Washington, DC, USA. Available online: https://library.si.edu/digital-library/book/activitiesrep19781
981regi (accessed on 23 November 2021).
3.
Harshbarger, J.C. Activities Report: Registry of Tumors in Lower Animals; 1965–1973; National Museum of Natural History:
Washington, DC, USA, 1974.
4.
Catão-Dias, J.L.; Nichols, D.K. Neoplasia in snakes at the National Zoological Park, Washington, DC (1978–1997). J. Comp. Pathol.
1999,120, 89–95. [CrossRef]
5. Lucke, B.; Schlumberger, H.C. Neoplasia in cold-blooded vertebrates. Physiol. Rev. 1949,29, 91–126. [CrossRef] [PubMed]
6.
Ramsay, E.C.; Munson, L.; Lowenstine, L.; Fowler, M.E. A Retrospective Study of Neoplasia in a Collection of Captive Snakes. J.
Zoo Wildl. Med. March 1996,27, 28–34.
7.
Christman, J.; Devau, M.; Wilson-Robles, H.; Hoppes, S.; Rech, R.; Russell, K.E.; Heatley, J.J. Oncology of Reptiles: Diseases,
Diagnosis, and Treatment. Vet. Clin. N. Am. Exot. Anim. Pract. 2017,20, 87–110. [CrossRef]
8.
Garner, M.M.; Hernandez-Divers, S.M.; Raymond, J.T. Reptile neoplasia: A retrospective study of case submissions to a specialty
diagnostic service. Vet. Clin. N. Am. Exot. Anim. Pract. 2004,7, 653–671. [CrossRef]
9.
Hernandez-Divers, S.M.; Garner, M.M. Neoplasia of reptiles with an emphasis on lizards. Vet. Clin. N. Am. Exot. Anim. Pract.
2003,6, 251–273. [CrossRef]
10.
Dietz, J.; Heckers, K.O.; Aupperle, H.; Pees, M. Cutaneous and Subcutaneous Soft Tissue Tumours in Snakes: A Retrospective
Study of 33 Cases. J. Comp. Pathol. 2016,155, 76–87. [CrossRef]
11.
Lamglait, B.; Lemberger, K. Colonic adenocarcinomas in a familial group of captive amur rat snakes (elaphe schrencki). J. Zoo
Wildl. Med. 2017,48, 491–496. [CrossRef]
12.
Sykes, J.M.; Trupkiewicz, J.G. Reptile neoplasia at the Philadelphia Zoological Garden, 1901–2002. J. Zoo Wildl. Med.
2006
,37,
11–19. [CrossRef]
13.
Kaye, S.W.; Daverio, H.; Eddy, R.; Ossiboff, R.J.; Peters-Kennedy, J.; Morrisey, J.K. Surgical resection of an interrenal cell
adenocarcinoma in a woma python (Aspidites ramsayi) with 18 month follow-up. J. Herpetol. Med. Surg.
2016
,26, 26–31.
[CrossRef]
14.
Summa, N.M.; Guzman, D.S.M.; Hawkins, M.G.; Grosset, C.; Chen, V.S.; Goldsmith, D.; Keel, K.; Woolard, K.; Young, A.C.; Bucy,
D.S.; et al. Tracheal and colonic resection and anastomosis in a boa constrictor (Boa constrictor) with T-cell lymphoma. J. Herpetol.
Med. Surg. 2015,25, 87–99. [CrossRef]
15. Hall, A.S.; Jacobs, J.L.; Smith, E.N. Possible osteosarcoma reported from a new world elapid snake and review of reptilian bony
tumors. Anat. Rec. 2020,303, 2955–2966. [CrossRef]
16.
Muñoz-Gutiérrez, J.F.; Garner, M.M.; Kiupel, M. Cutaneous Chromatophoromas in Captive Snakes. Vet. Pathol.
2016
,53,
1213–1219. [CrossRef]
17.
Page-Karjian, A.; Hahne, M.; Leach, K.; Murphy, H.; Lock, B.; Rivera, S. Neoplasia in snakes at zoo atlanta during 1992–2012. J.
Zoo Wildl. Med. 2017,48, 521–524. [CrossRef]
18. Pereira, M.E.; Viner, T.C. Oviduct adenocarcinoma in some species of captive snakes. Vet. Pathol. 2008,45, 693–697. [CrossRef]
19.
Taggart, P.L.; Woolford, L.; Dunstan, N.; Allen, L.; Buote, M.; Lindsay, S.A. Cutaneous Chromatophoromas in Four Species of
Australian Elapid Snake. J. Comp. Pathol. 2021,183, 33–38. [CrossRef]
20. Elkan, E.; Cooper, J.E. Tumours and pseudotumours in some reptiles. J. Comp. Pathol. 1976,86, 337–348. [CrossRef]
21.
Anderson, E.T.; Kennedy-Stoskopf, S.; Sandy, J.R.; Dorn, B.; Boyette, T.; Harms, C.A. Squamous cell carcinoma with vascular
invasion in a diamondback rattlesnake (Crotalus adamanteus). J. Zoo Wildl. Med. 2010,41, 745–748. [CrossRef] [PubMed]
22. Frye, F.L. Diagnosis and surgical treatment of reptilian neoplasms with a compilation of cases 1966–1993. Vivo 1994,8, 885–892.
23.
Harris, P.; Taylor, R.; Minor, B.; Elliott, V.; Fernandez, M.; O’Neal, L.; McLeod, L.; Delacqua, G.; Delacqua, F.; Kirby, J.; et al. The
REDCap consortium: Building an international community of software partners. J. Biomed. Inform.
2019
,95, 103208. [CrossRef]
[PubMed]
24.
Harris, P.; Taylor, R.; Thielke, R.; Payne, J.; Gonzalez, N.; Conde, J. Research electronic data capture (REDCap)—A metadata-driven
methodology and workflow process for providing translational research informatics support. J. Biomed. Inform.
2009
,42, 377–381.
[CrossRef] [PubMed]
25. IBM Corp. IBM SPSS Statistics for Windows, 26.0; IBM Corp: Armonk, NY, USA, 2019.

Animals 2022,12, 258 17 of 17
26.
Team, R.C. R: A Language and Environment for Statistical Computing; R Foundation for Statistical Computing: Vienna, Austria, 2019.
27.
Kassambara, A.; Kosinski, M.; Biecek, P. Survminer: Drawing Survival Curves Using ‘ggplot2’. R package version 0.4.9. 2021.
Available online: https://CRAN.R- project.org/package=survminer (accessed on 18 January 2022).
28.
Therneau, T. A Package for Survival Analysis in S. version 2.38. 2015. Available online: https://CRAN.R-project.org/package=
survival (accessed on 18 January 2022).
29.
Hothorn, T.; Buehlmann, P.; Kneib, T.; Schmid, M.; Hofner, B. M Boost: Model-Based Boosting. R package version 2.6.0. 2018.
Available online: https://CRAN.R- project.org/package=mboost (accessed on 18 January 2022).
30.
Mayr, A.; Hofner, B.; Waldmann, E.; Hepp, T.; Meyer, S.; Gefeller, O. An Update on Statistical Boosting in Biomedicine. Comput.
Math. Methods Med. 2017,2017, 6083072. [CrossRef] [PubMed]
31. Baron, H.R.; Allavena, R.; Melville, L.M.; Doneley, R.J.T. Gastric adenocarcinoma in a diamond python (Morelia spilota spilota).
Aust. Vet. J. 2014,92, 405–409. [CrossRef]
32.
Steeil, J.C.; Schumacher, J.; Hecht, S.; Baine, K.; Ramsay, E.C.; Ferguson, S.; Miller, D.; Lee, N.D. Diagnosis and treatment of a
pharyngeal squamous cell carcinoma in a Madagascar ground boa (Boa madagascariensis). J. Zoo Wildl. Med.
2013
,44, 144–151.
[CrossRef] [PubMed]
33.
Diethelm, G.; Stauber, E.; Tillson, M.; Ridgley, S. Tracheal resection and anastomosis for an intratracheal chondroma in a ball
python. J. Am. Vet. Med. Assoc. 1996,209, 786–788.
34.
Hopewell, E.; Harrison, S.H.; Posey, R.; Duke, E.; Troan, B.; Harrison, T.M. Analysis of Published Amphibian Neoplasia Case
Reports. J. Herpetol. Med. Surg. 2020,30, 148–155. [CrossRef]
35.
Bryant, B.R.; Vogelnest, L.; Hulst, F. The use of cryosurgery in a diamond python, Morelia spilota spilota, with fibrosarcoma and
radiotherapy in a common death adder, Acanthophis antarcticus, with melanoma. Bull. Assoc. Reptil. Amphib. Vet.
1997
,7, 9–12.
[CrossRef]