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Sex with Animals (SWA): Behavioral Characteristics and Possible
Association with Penile Cancer. A Multicenter Studyjsm_25121..8
Stênio de Cássio Zequi, PhD,* Gustavo Cardoso Guimarães, PhD,*
Francisco Paulo da Fonseca, PhD,* Ubirajara Ferreira, PhD,†Wagner Eduardo de Matheus, PhD,†
Leonardo Oliveira Reis, MD,†Giuliano Amorim Aita, MD,‡Sidney Glina, PhD,§
Victor Silvestre Soares Fanni, MD,§Marjo Denisson Cardenuto Perez, PhD,¶
Luiz Renato Montez Guidoni, MD,¶Valdemar Ortiz, PhD,** Lucas Nogueira, MD,††
Luis Carlos de Almeida Rocha, PhD,‡‡ Gustavo Cuck, MD,§§ Walter Henriques da Costa, MD,¶¶
Ravendra Ryan Moniz, MD,¶¶ José Hipólito Dantas Jr., MD,*** Fernando Augusto Soares, PhD,††† and
Ademar Lopes, PhD*
*Urology Division of Pelvic Surgery Department, Hospital A C Camargo, São Paulo, SP, Brazil; †Urology Division,
UNICAMP Universidade Estadual de Campinas, Campinas, SP, Brazil; ‡Urologic Department, Hospital São Marcus,
Teresina, PI, Brazil; §Urology Division, Hospital Ipiranga, São Paulo, SP, Brazil; ¶Urology Division of Surgical Department
FCMSCSP, Faculdade de Ciências Médicas da Santa Casa de São Paulo, SP, Brazil; **Urology Department, UNIFESP,
Universidade Federal de São Paulo, São Paulo, SP, Brazil; ††Urology Department, UFMG, Universidade Federal de
Minas Gerais, Belo Horizonte, MG, Brazil; ‡‡Urology Department, Hospital das Clínicas da UFPR, Universidade Federal
do Paraná, Curitiba, PR, Brazil; §§Urology Division, Hospital da Aeronáutica de São Paulo, SP, Brazil; ¶¶Urology Service,
Hospital, Geral de Carapicuíba, SP, Brazil; ***Genitourinary Diseases Disciplin, Hospital Universitário Onofre Lopes,
UFRN, Universidade Federal do Rio Grande do Norte, RN, Brazil; †††Surgical and Investigative Pathology Department,
Hospital A C Camargo, São Paulo, SP, Brazil
DOI: 10.1111/j.1743-6109.2011.02512.x
ABSTRACT
Introduction. Zoophilia has been known for a long time but, underreported in the medical literature, is likely a risk
factor for human urological diseases.
Aim. To investigate the behavioral characteristics of sex with animals (SWA) and its associations with penile cancer
(PC) in a case-control study.
Methods. A questionnaire about personal and sexual habits was completed in interviews of 118 PC patients and 374
controls (healthy men) recruited between 2009 and 2010 from 16 urology and oncology centers.
Main Outcome Measures. SWA rates, geographic distribution, duration, frequency, animals involved, and behav-
ioral habits were investigated and used to estimate the odds of SWA as a PC risk factor.
Results. SWA was reported by 171 (34.8%) subjects, 44.9% of PC patients and 31.6% of controls (P<0.008). The
mean ages at first and last SWA episode were 13.5 years (standard deviation [SD] 4.4 years) and 17.1 years (SD 5.3
years), respectively. Subjects who reported SWA also reported more venereal diseases (P<0.001) and sex with
prostitutes (P<0.001), and were more likely to have had more than 10 lifetime sexual partners (P<0.001) than those
who did not report SWA. SWA with a group of men was reported by 29.8% of subjects and SWA alone was reported
by 70.2%. Several animals were used by 62% of subjects, and 38% always used the same animal. The frequency of
SWA included single (14%), weekly or more (39.5%), and monthly episodes (15%). Univariate analysis identified
phimosis, penile premalignancies, smoking, nonwhite race, sex with prostitutes, and SWA as PC risk factors.
Phimosis, premalignant lesions, smoking, and SWA remained as risk factors in multivariate analysis. However, SWA
did not impact the clinicopathological outcomes of PC.
Conclusion. SWA is a risk factor for PC and may be associated with venereal diseases. New studies are required in
other populations to test other possible nosological links with SWA. Zequi SC, Guimarães GC, da Fonseca FP,
Ferreira U, de Matheus WE, Reis LO, Aita GA, Glina S, Fanni VSS, Perez MDC, Guidoni LRM, Ortiz V,
Nogueira L, Rocha LCA, Cuck G, da Costa WH, Moniz RR, Dantas Jr. JH, Soares FA, and Lopes A. Sex with
animals (SWA): Behavioral characteristics and possible association with penile cancer. A multicenter study.
J Sex Med **;**:**–**.
Key Words. Sex with Animals; Bestiality; Penile Cancer; Zoophilia; Risk Factor; Sexually Transmitted Diseases;
HPV
1
© 2011 International Society for Sexual Medicine J Sex Med **;**:**–**
Introduction
Penile cancer (PC) is rare in the developed
world but frequent in poor regions [1]. Risk
factors for PC include unfavorable hygiene,
poverty, chronic balanopreputial irritation, prema-
lignant penile lesions, and smoking [2]. Human
papillomavirus (HPV) infection is associated with
approximately half of PC cases, but its role in PC
carcinogenesis has not been clearly established [3].
The role of promiscuity and other sexually trans-
mitted diseases (STDs) in PC is also not com-
pletely understood [4].
The present case-control study investigated
whether a personal history of sex with animals
(SWA), which is a common male sexual practice in
rural areas with high PC prevalence, plays a role in
PC. We also describe clinical and demographic
characteristics of this sexual behavior.
Materials and Methods
Study Design and Subjects
Data were collected at 16 tertiary urology or oncol-
ogy centers in 12 Brazilian cities (Table 1). The
subjects included new PC cases and patients previ-
ously treated for PC, all of whom were enrolled by
mail or by phone. The control group was composed
of healthy males aged 18 to 80 years seeking
medical attention for benign uropathies, check-up
or for cancer prevention. We ascertained that
control subjects lived in rural zones during child-
hood and adolescence and were exposed to animal-
contact hazards. Individuals who grew up in an
urban environment were excluded. A questionnaire
about personal and sexual habits was completed by
all subjects via an in-person semi-structured inter-
view with their physicians. This study was approved
by our institutional review boards. All subjects pro-
vided written informed consent.
The selected variables were race, age at enroll-
ment, age of first sexual relationship, history of
STD (urethritis, gonorrhea, syphilis, condyloma
acuminata, HIV infection), penile premalignant
lesions (Queyrat’s erythroplasia, Bowen’s disease,
lichen sclerosis, balanitis xerotica obliterans,
chronic balanitis), phimosis and circumcision, age
at circumcision, number of lifetime sexual partners,
smoking habits (past or current), history of sex with
prostitutes, and SWA. The SWA questions
addressed age at first and last SWA episodes, the
frequency of SWA (in days, weeks, months), and the
duration of SWA practice in complete years (com-
puted by subtracting the age at the first SWA
episode from the age at the last SWA episode, but
only if SWA duration was more than 1 year). We
investigated the animal species involved and
whether SWA was performed individually or in a
group of men, and whether SWA always occurred
with the same animal or with several animals.
Clinicopathological data for premalignant
lesions and PC (histological type, grade, 2002
TNM/UICC [5] (International Union Against
Cancer) staging, and therapeutic modality) were
obtained from medical records. A central office
managed the data bank and statistical analyses
using Statistical Package for the Social Sciences
version 15 (SPSS Inc., Chicago, IL, USA).
Statistical Analysis
Questionnaire responses from a total of 492 sub-
jects, 118 PC patients and 374 controls (3.16 con-
trols per case), were compared using logistic
regression analysis to calculate exposure odds
ratios (OR) and 95% confidence intervals (CIs) for
both groups. The modeling results reflect adjusted
incidence rate ratios. Proportions were deter-
mined using the c2test or Fisher’s exact test. Two-
sided Pvalues <0.05 and 95% CI were considered
indicators of significance. Differences in age were
Table 1 The rates of sex with animals (SWA) in Brazilian states, cities, and geographical regions
States (cities) N
Geographic
region†
Reporting
SWA (%) No SWA (%)
São Paulo* (São Paulo, Campinas, Barretos, Itapevi, Carapicuíba) 287 Southeast 94 (32.8) 193 (67.2)
Minas Gerais (Belo Horizonte) 29 Southeast 11 (37.9) 18 (62.1)
Piauí (Teresina) 53 Northeast 34 (64.2) 19 (35.8)
Maranhão (São Luís) 14 Northeast 8 (57.1) 6 (42.9)
Rio Grande do Norte (Natal) 28 Northeast 8 (28.6) 20 (71.4)
Paraíba (João Pessoa) 15 Northeast 4 (26.7) 11 (73.3)
Acre (Rio Branco) 20 North 6 (30) 14 (70)
Paraná (Curitiba) 46 South 6 (13) 40 (87)
Total 492 — 171 (34.8) 321 (65.2)
*Nine hospitals participated from cities in São Paulo state.
†The rates of SWA were 45%, 33.2%, 20%, and 13% in the northeast, southeast, north, and south, respectively.
2Zequi et al.
J Sex Med **;**:**–**
tested using Student’s t-test. All significant
explanatory variables in the univariate analysis
were entered simultaneously into a logistic regres-
sion model. We arrived at a multivariate model
using backward elimination to remove the least
significant variables one-by-one until all remain-
ing variables in the model were significant
(P<0.05 in test for homogeneity). Subsequently,
excluded explanatory variables were given another
chance to enter the final model via forward inclu-
sion, but none of the variables previously excluded
achieved statistical significance.
Results
The majority of subjects (80.1%) were uncircum-
cised; 13.4% were circumcised as adults, 3.7% in
adolescence, and 2.8% in infancy. The PC and
control groups were homogeneous according to
age (Table 2). The PC group included more non-
whites (51.8% vs. 36.6%; P=0.006) and higher
rates of smoking (70.3% vs. 45.7%; P<0.001),
phimosis (67.8% vs. 14.4%; P<0.001), sex with
prostitutes (73.7% vs. 63.9%; P=0.049), prema-
lignant lesions, and SWA compared to the control
group (Table 2).
In the PC group, the rates of premalignant
lesions were 30.3%: 16% balanitis xerotica oblit-
erans, 12.7% chronic balanitis, 0.8% Queyrat’s
erythroplasia, and 0.8% Bowen’s disease. In the
control group, the rates of premalignancies were
4.7% (P<0.001):1.4% balanitis xerotica obliter-
ans, 2.7% chronic balanitis, 0.3% Bowen’s disease,
and 0.3% lichen sclerosis.
A total of 171 individuals (34.8%) reported
SWA (Table 1), which was more common among
PC patients (44.9%) than controls (31.6%;
P=0.008; Table 2), and among individuals with a
history of STDs than those without STDs (56.7%
vs. 43.3%; P<0.001). Subjects who reported SWA
also reported more sex with prostitutes (79.5% vs.
59.2%; P<0.001) and were more likely to have
had >10 lifetime sexual partners (64.3% vs. 44.8%;
P<0.001) compared to those who did not report
SWA. Penile premalignant lesions occurred in
14.9% of individuals with a history of SWA and in
9% of those without a history of SWA (P=0.088).
Smoking rates among individuals reporting SWA
were 56.7% vs. 48.6% for those who did not
report SWA (P=0.086).
The mean ages at first and last SWA episode
were 13.5 years (standard deviation [SD] 4.4 years)
and 17.1 years (SD 5.3 years), respectively. The
mean ages at sexual debut with humans were 16.3
years (SD 7.3 years) and 16.7 years (SD 3.6 years)
for subjects who did and did not report SWA,
respectively. Independent of SWA status, age at
first intercourse with humans was similar between
Table 2 Univariate analysis of penile cancer (PC) risks
Variable Category N PC cases (%) Controls (%) Pvalue*
Age, years Mean 57.57 (SD 14.49) Mean 58.72 (SD 13.00) Mean 57.20 (SD 14.93) 0.2972†
Median: 59 Median: 58.0 Median: 59
Min: 18 Min: 25 Min: 18
Max: 90 Max: 85 Max: 90
Race White 295 58 (19.7) 237 (80.3) 0.036
Black 64 23 (35.9) 41 (64.1)
Mulato 122 34 (27.9) 88 (72.1)
Asiatic 11 03 (27.3) 08 (72.7)
History of sexually transmitted disease Yes 227 62 (27.3) 165 (72.7) 0.068
No 265 56 (21.1) 209 (78.9)
Penile premalignant lesions Yes 53 36 (67.9) 17 (32.1) <0.001
No 439 82 (18.7) 357 (81.3)
Smoking Yes 253 83 (32.7) 171 (67.3) <0.001
No 239 35 (14.7) 203 (85.3)
Phimosis Yes 134 80 (59.7) 54 (40.3) <0.001
No 358 38 (10.6) 320 (89.4)
Sex with prostitutes Yes 326 87 (27.3) 239 (72.7) 0.033
No 166 31 (18.7) 135 (81.3)
Number of sexual partners ⱕ10 237 50 (21.1) 187 (78.9) 0.090
>10 255 68 (26.7) 187 (73.3)
Sex with animals Yes 171 53 (31.0) 118 (69.0) 0.008
No 321 65 (20.2) 256 (79.8)
*c2test.
†Student’s t-test for age.
Sex with Animals (SWA) and Penile Cancer 3
J Sex Med **;**:**–**
PC patients (17.0 years; SD 8.4 years) and controls
(16.5 years; SD 3.7 years).
SWA periodicity varied. A single SWA lifetime
episode was reported by 14% of SWA-reporting
subjects. SWA episodes were reported at frequen-
cies of twice per month (17%), monthly (15.2%),
weekly (10.5%), three times per week (10%), twice
per week (9.4%), daily (4.1%), and every other day
(5.3%). Bimonthly, semiannual, and quarterly
SWA was reported by 3.5%, 2.9%, and 2.3%,
respectively. In two cases (1.2%), the frequency
was not reported.
The duration of SWA behavior was less than 1
year in 34 individuals (19.9%). In the 137 subjects
(80.1%), it ranged from 1 to 26 years (mean 4.47
years, SD 3.8 years; median 3.0 years). Durations
of 1 to 5 years were reported by 101 individuals
(59%), and 36 subjects (21.1%) described SWA
behavior as persisting for more than 5 years. High
SWA periodicity (daily, alternate days, three or
more times per week, twice per week, biweekly,
and monthly) and long-term SWA were associ-
ated; 87.2% of individuals reporting >3 years of
SWA also reported high-periodicity SWA, com-
pared with 55.3% of those reporting <3 years of
SWA (P<0.001).
SWA with a group of men was reported by
29.8% of SWA-reporting study participants, with
similar rates reported by PC patients (34%) and
controls (28%; P=0.396). SWA was practiced
with the same animal by 38.0% of SWA practitio-
ners, with similar rates reported by PC patients
and controls (34% vs. 39.8%, respectively;
P=0.638). The number of animals involved per
individual ranged from 1 to 7. The animal types
most often cited were mares (N =80), followed by
donkeys (N =73), mules (N =57), goats (N =54),
chickens (N =27), calves (N =18), cows (N =13),
dogs (N =10), sheep (N =10), pigs (N =6), and
other species (N =3). Chickens were more fre-
quently involved in the south and southeast of the
country, with only three reports in the northeast,
where donkeys dominated the reports. Higher
SWA rates were found in the northeast (45%),
with the highest rates in Piauí and Maranhão
(Table 1).
Among the 171 men who reported SWA, 50
(29.2%) had PC. In these men, no association was
detected between PC and the number of animals
(always the same animal vs. several animals,
P=0.417), species (P=0.679), or the number of
people involved (SWA alone or in a group,
P=0.290). Individualized SWA periodicities were
not associated with PC (P=0.19). In addition,
high or low SWA periodicity was not associated
with PC. High SWA periodicity was reported by
78% of the PC patients and 68.1% of the controls
(P=0.263). Long-term SWA (>3 years) was
reported by 64% of the PC patients and 46.6% of
the controls (P=0.044). The predominant PC his-
tology was squamous cell carcinoma (50.8% well-
differentiated, 29.6% moderately differentiated,
and 11% undifferentiated). Carcinoma in situ, ver-
rucous carcinoma, sarcoma, and other forms
occurred in 2.5%, 3.4%, 0.8%, and 1.9% of PC
cases, respectively. Low grade (I/II), high grade
(III/IV), and unspecified ignored grade were indi-
cated in 76.7%, 13.8%, and 9.5% of cases, respec-
tively. Superficial tumors occurred in 55.1% of PC
cases (pTa or pTis in 6.8% and pT1 in 48.3%) and
invasive tumors (ⱖpT2) in 44.9% of PC cases.
Negative inguinal lymph nodes occurred in
72.9% of cases. Three patients (2.5%) had distant
metastases. Primary tumor treatments included
partial penile amputation (72%), total penile
amputation (10%), tumor exeresis or postectomy
(8.5%), and other treatments (9.5%). Eighty-nine
patients (75.4%) were alive without disease, and 29
(25.6%) were alive with cancer at the time of the
study.
SWA behavior was not significantly associated
with histological type (P=0.201), grade
(P=0.310), treatment (P=0.346), pT stage
(P=0.857), pN stage (P=0.177), pM stage
(P=0.270), or clinical status (P=0.396). Univari-
ate analysis (Table 2) revealed the following risk
factors for PC: phimosis (P<0.001), premalignant
lesions (P<0.001), smoking (P<0.001), SWA
(P=0.008), race (white vs. nonwhite; P=0.007),
and sex with prostitutes (P=0.033). In the multi-
variate analysis (Table 3), phimosis (OR 10.41,
95% CI 6.12–17.67; P<0.001), premalignant
lesions (OR 3.90, 95% CI 1.88–8.09; P<0.001),
smoking (OR 2.71, 95% CI 1.59–4.62; P<0.001),
and SWA (OR 2.07, 95% CI 1.21–3.52; P=0.007)
were risk factors for PC.
Discussion
The practice of having SWA has been present
since ancient times [6]. SWA is underreported in
the medical literature, but has been transmitted
through oral traditions, it is present in artistic rep-
resentations, and was prohibited by the Bible
(Exod 22:28; Lev 20:16) [6–8]. This behavior may
be interpreted as curiosity or as experiences pre-
ceding male sexual maturity [9]. Kinsey reported
that 8% of Americans had some SWA experience,
4Zequi et al.
J Sex Med **;**:**–**
and affirmed that SWA is common among teen
farmers of low intelligence [10]. Others consider
SWA as something other than a simple substitutive
phenomenon, such as a psychopathic manifesta-
tion of neurosis or psychosis [8].
In small samples of psychiatric inpatients,
medical inpatients, and psychiatric staff, the preva-
lence of bestiality (sexual contact or only fantasy)
was 55%, 10%, and 15%, respectively, but sexual
contact was verified only among male psychiatric
inpatients. All groups had similar SWA fantasy
rates [11].
In this population, the majority of subjects
reporting SWA stopped the practice around the
period that they began sexual contact with
humans; thus, in the context of the present study,
SWA must be distinguished from established bes-
tiality or zoophilia, paraphilias represented by
continuous or obsessive desires for SWA instead
of sex with human partners [5,7,9]. An online
questionnaire with 114 self-defined zoophiles
in developed countries revealed that 36% lived
in large cities and 83% were either college gradu-
ates or had completed some college. Forty-
five percent of the respondents worked in infor-
matics or technology, some of them with high
income [6]. However, third-world PC patients
exhibit the opposite socioeconomic and cultural
characteristics.
The motivation for this study came from the
observation that the majority of PC patients origi-
nate from poor rural zones, a typical environment
for SWA occurrence. This rural determinant was
used as a main condition in recruiting the control
population. We excluded men that grew up in an
urban environment, because PC prevalence is
anecdotal in these regions, suggesting that this
population is at little risk of developing this malig-
nancy. Furthermore, the opportunities for an
urban teenager to be in contact with animals in a
situation allowing sexual activity are restricted. In
contrast, boys in rural areas live daily with animals,
with several opportunities of having sexual contact
with them. Thus, by choosing individuals from
rural areas, we ensured that both cases and con-
trols were under the same odds of intimate contact
with animals and faced with the same decisions
regarding consummation.
In addition, the homogeneity of age between
PC patients and control subjects was fundamental.
In the last few decades, sexual freedom has favored
earlier sexual contacts, probably reducing sexual
contact with animals. An age bias would thus have
introduced additional biases into the investigation.
Our study relied on in-person semi-structured
interviews because many of the study participants
are illiterate or partially literate, which would
compromise comprehension of the questionnaire.
Although other biases may be introduced by this
format, such as inhibition or lying, the anonymity
of web-based or written questionnaires does not
imply total veracity.
SWA emerged as a risk factor for PC in the
multivariate analysis (Table 3). We hypothesize
that SWA promotes contact of penile tissues with
foreign genital mucosa, resulting in microtrauma
and exposure to the animals’ anogenital secretions,
which may be antigenic or carcinogenic for
humans. This situation would favor chronic irrita-
tion processes and subsequent dysplasia. Penile
injuries, tears, abrasions, or balanitis are known to
increase PC risk [2,4,12–16].
Additionally, 51.4% of the study population
smoked, 14% of SWA participants had premalig-
nancies, and the majority of subjects were uncir-
cumcised or circumcised later in life. This
situation is associated with other environmental
PC risk factors, such as poor hygienic conditions,
poverty, and HPV infection [2,4,12–18], which
may potentiate conditions for PC development.
The link between SWA and PC and its associa-
tion with STDs may reflect the SWA practitioners’
lifestyle. The subjects that reported SWA had
more sex with prostitutes, more sexual partners,
and more STDs than subjects who did not report
SWA; moreover, 29.8% of them practiced SWA
with a group of men, 64.9% had sex with multiple
animals.
Table 3 Multivariate analysis of penile cancer risk factors
Variable Odds ratio 95% confidence interval Pvalue
Phimosis 10.41 6.12–17.67 <0.001
Penile premalignant lesions 3.90 1.88–8.09 <0.001
Smoking 2.71 1.59–4.62 <0.001
Sex with animals 2.07 1.21–3.52 0.007
Race (nonwhite vs. white) 0.63 0.375–1.05 0.078
Sex with prostitutes 0.83 0.46–1.47 0.514
Sex with Animals (SWA) and Penile Cancer 5
J Sex Med **;**:**–**
We identified a high rate of uncircumcised
men with PC, although the role of unknown
infectious agents (virus, bacteria, or other micro-
organisms) [9,19] in interspecies sexual contact
can not be completely discarded. Some neoplasias
are associated with infections, such as links
between uterine cervical cancer or anogenital car-
cinomas and HPV infections or gastric carcinoma
and presence of Helicobacter pylori [19,20]. Recent
reports have also described a possible pathogenic
role of XMRV retrovirus [21,22] in prostate
cancer, another genital organ neoplasia, as well as
a role of prions in tumorigenesis [23]. The penis
may also be susceptible to infections in addition
to HPV. Prolonged and continuous SWA expo-
sure in our study population (60% practiced
SWA over 1–5 years and 20% for more than 5
years, many of them several times a month or
weekly) would increase the opportunities for
penile microtrauma and may facilitate exposure
to infectious agents present in the external
environment.
Speculation exists regarding cancer status as an
infectious disease in humans [24,25], as studies
have suggested that tumor cells can be transmitted
from one mammal host to another within the same
species [26,27]. PC is frequent in equines [28], but
transmission of malignancies between animals and
humans has not been reported. Virology does not
consider possible viral movement from animals to
humans except in cases of zoonosis, such as rabies
or pandemic forms of bird or swine flu. However,
the hypothesis that the HIV epidemic resulted
from simian–human virus transmission has not
been fully explored [29].
Fewer southern and northern Brazilian institu-
tions were evaluated because PC is rare in the
south [17] and the north has low population
density. SWA was more frequent in the poorest
Brazilian region, the northeast, and the rates were
lowest in the southern region, which is developed
and urbanized (Table 1). The kind of animals
involved in SWA varied according to the domestic
species that are typical of each region. The use of
the same animal by 34.5% of SWA participants
may be due to poverty, as the individual only has
one animal, or some affective relationship with the
animal.
This study was hindered by a few limitations.
We did not investigate the sexual orientation of
the SWA practitioners regarding animals or
human partners. For example, how many of these
men were engaging in sex with men? In what types
of sexual activity did the SWA-positive men and
the animals engage? We assumed that our study
subjects penetrated the animal vaginally or anally;
we did not investigate other possibilities. We did
not evaluate condom use, but we think that during
the period in which these patients participated in
SWA (before the “AIDS era”), condom use was
not as widespread as it is nowadays. Specific patho-
logical features or clinical outcomes of PC were
not detected in the sample, probably due to the
sample size and the nature of the retrospective data
from several institutions with different treatment
protocols. A central pathological review in associa-
tion with a molecular investigation of HPV in a
large PC cohort is underway.
Our findings were based on self-reported
history of SWA. Since self-report surveys may be
questionable and are subject to recall bias, the ideal
would be to design observational prospective
cohort studies. However, we reiterate the several
technical and ethical difficulties involved in a study
of this nature on this issue, beyond the assumption
that the practice of SWA could put patients under
risk of morbid conditions.
Although this study reflects the sexual practices
of a population that occurred decades ago (espe-
cially during the adolescence of the subjects), SWA
is a worldwide practice. There are several zoo-
philic associations or clubs in developed countries
[7] and many “zoo” web sites and virtual commu-
nities on the Internet [6] that are frequently asso-
ciated with pornographic content, and may
constitute a global health concern. Studies must be
performed in several countries and civilizations
with different incidences of PC and STDs, as well
as on rural, indigenous and urban communities, on
females, and in urological cancer facilities. Con-
sidering future prevention strategies, investiga-
tions of SWA in Africa would be interesting, as
studies have already demonstrated a protective
role of male circumcision against several STDs
[30–32]. Novel possible associations between
SWA and urological diseases might be tested,
including non-traumatic urethral stenosis, idio-
pathic infertility, and chronic prostatitis. Health
campaigns should be discussed to promote the
refutation of SWA in target populations. In
extreme refractory cases, condom use or other
barrier methods should be suggested to minimize
the risks of this sexual option, although this is
ethically debatable.
SWA merits serious scientific attention due to
its high prevalence and associated risks for PC and
perhaps STDs. Initiatives to eradicate SWA
should be considered.
6Zequi et al.
J Sex Med **;**:**–**
Acknowledgments
The authors thank the Penile Cancer Study Group
(PCSG) members: Sandro Nassar Cardoso, MD
(Urology Division, Hospital Ipiranga, São Paulo, SP,
Brazil), Roni de Carvalho Fernandes, MD (Urology Divi-
sion of Surgical Department FCMSCSP, Faculdade de
Ciências Médicas da Santa Casa de São Paulo, SP, Brazil),
Jose Vassalo, PhD (Surgical and Investigative Pathology
Department, HospitalACCamargo, São Paulo, SP,
Brazil), Fernando Assis Melo, MD (Urology Service,
FUNDACRE, Fundação Hospitalar do Acre, Rio Branco,
AC, Brazil), José Ribamar Rodrigues Calixto, MD
(Urology Departament, Hospital Universitário da Uni-
versidade Federal do Maranhão, MA, Brazil), Marcus
Mattos, MD (Urology Service, Hospital Geral de Itapevi,
SP, Brazil), Daniel Damião Gomes Seabra, PhD (Urology
Department, Hospital do Câncer de Barretos, Fundação
Pio XII, Barretos, SP, Brazil), Cristiano Utida, MD
(Urology Department, UNIFESP, Universidade Federal
de São Paulo, São Paulo, SP, Brazil), Fábio Martinez de
Melo, MD (Urology Division, Hospital Napoleão Laure-
ano, João Pessoa, PB, Brazil), Djalma de Carvalho
Moreira Filho, PhD (Public Health and Preventive Medi-
cine Department of UNICAMP, Universidade Estadual
de Campinas, Brazil).
Corresponding Author: Stênio de Cássio Zequi, PhD,
Urology Division of Pelvic Surgery Department, Hos-
pital A C Camargo, Rua Professor Antônio Prudente,
211, São Paulo 01509 010, Brazil. Tel: 5511 2189 5000;
Fax: 5511 38849103; E-mail: steniozequi@uol.com.br,
steniozequi@gmail.com
Conflict of Interest: None.
Statement of Authorship
Category 1
(a) Conception and Design
Stênio de Cássio Zequi
(b) Acquisition of Data
Stênio de Cássio Zequi; Wagner Eduardo de
Matheus; Leonardo Oliveira Reis; Giuliano
Amorim Aita; Victor Silvestre Soares Fanni; Luiz
Renato Montez Guidoni; Lucas Nogueira; Gustavo
Cuck; Walter Henriques da Costa; Ravendra Ryan
Moniz; José Hipólito Dantas Jr.
(c) Analysis and Interpretation of Data
Stênio de Cássio Zequi; Gustavo Cardoso Guima-
rães; Francisco Paulo da Fonseca; Leonardo
Oliveira Reis; Giuliano Amorim Aita; Sidney Glina;
Valdemar Ortiz; Luis Carlos de Almeida Rocha;
Fernando Augusto Soares; Marjo Denisson Carde-
nuto Perez; Ademar Lopes
Category 2
(a) Drafting the Article
Stênio de Cássio Zequi; Gustavo Cardoso Guima-
rães; Leonardo Oliveira Reis; Francisco Paulo da
Fonseca; Ademar Lopes; Fernando Augusto Soares;
Sidney Glina; Wagner Eduardo de Matheus;
Gustavo Cuck; Walter Henriques da Costa
(b) Revising It for Intellectual Content
Stênio de Cássio Zequi; Ubirajara Ferreira;
Giuliano Amorim Aita; Victor Silvestre Soares
Fanni; Marjo Denisson Cardenuto Perez; Luiz
Renato Montez Guidoni; Valdemar Ortiz; Lucas
Nogueira; Luis Carlos de Almeida Rocha; Ravendra
Ryan Moniz; José Hipólito Dantas Jr.
Category 3
(a) Final Approval of the Completed Article
Stênio de Cássio Zequi; Gustavo Cardoso Guima-
rães; Francisco Paulo da Fonseca; Ubirajara Fer-
reira; Wagner Eduardo de Matheus; Leonardo
Oliveira Reis; Giuliano Amorim Aita; Sidney Glina;
Victor Silvestre Soares Fanni; Marjo Denisson
Cardenuto Perez; Luiz Renato Montez Guidoni;
Valdemar Ortiz; Lucas Nogueira; Luis Carlos de
Almeida Rocha; Gustavo Cuck; Ravendra Ryan
Moniz; José Hipólito Dantas Jr.; Fernando Augusto
Soares; Ademar Lopes
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