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Embryonal Rhabdomyosarcoma in a Rothschild's Giraffe (Giraffa camelopardalis rothschildi)

  • Nashville Zoo at Grassmere

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Abstract: A 3-yr-old male Rothschild's giraffe (Giraffa camelopardalis rothschildi) presented for acute swelling caudomedial to the left parietal horn. Following initial diagnostics and supportive treatment, the mass was surgically resected and intralesional chemotherapy was administered. Despite treatment, the giraffe's condition worsened and euthanasia was performed. Gross necropsy revealed neoplastic invasion and destruction of underlying parietal bone, adjacent horn base, and sinuses, and metastases in the tracheobronchial and mandibular lymph nodes and lung. Histologically, the tumor was composed of packets of anaplastic round cells. Immunohistochemical studies further characterized the tumor as an embryonal rhabdomyosarcoma. This is the first reported case of rhabdomyosarcoma in a giraffe.
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Margarita Woc-Colburn, D.V.M., Suzan Murray, D.V.M., Dipl. A.C.Z.M., Nancy Boedeker, D.V.M.,
Tabitha Viner, D.V.M., Dipl. A.C.V.P., Michelle L. Fleetwood, D.V.M., Dipl. A.C.V.P., Tony
C. Barthel, Kurt D. Newman, M.D., and Carlos R. Sanchez, D.V.M., MSc.
Abstract: A 3-yr-old male Rothschild’s giraffe (Giraffa camelopardalis rothschildi) presented for acute swelling
caudomedial to the left parietal horn. Following initial diagnostics and supportive treatment, the mass was
surgically resected and intralesional chemotherapy was administered. Despite treatment, the giraffe’s condition
worsened and euthanasia was performed. Gross necropsy revealed neoplastic invasion and destruction of
underlying parietal bone, adjacent horn base, and sinuses, and metastases in the tracheobronchial and mandibular
lymph nodes and lung. Histologically, the tumor was composed of packets of anaplastic round cells.
Immunohistochemical studies further characterized the tumor as an embryonal rhabdomyosarcoma. This is the
first reported case of rhabdomyosarcoma in a giraffe.
Key words: Rothschild’s giraffe, Giraffa camelopardalis rothschildi, embryonal rhabdomyosarcoma.
Rhabdomyosarcomas arise from either striated
muscle or muscle progenitor cells.
tumors are classified into three main types based
on histopathologic features; namely embryonal,
alveolar, and pleomorphic. The reported inci-
dence of rhabdomyosarcomas in domestic ani-
mals is less than 1%of all neoplasias, most of
which are reported in dogs.
No sex or
age predisposition has been observed; however,
botryoid embryonal subtypes are most common-
ly found in the urinary bladder of juvenile large-
breed dogs.
In zoo animals, rhabdomyosar-
comas have been reported in Baird’s tapir
(Tapirus bairdii), fallow deer (Dama dama)and
white-tailed deer (Odocoileus virginianus).
following is the first reported case of an
embryonal rhabdomyosarcoma in a young
Rothschild’s giraffe (Giraffa camelopardalis
A 3-yr-old, male, 666-kg Rothschild’s giraffe
presented for an acute swelling around the left
parietal horn. Examination revealed a 3-cm
diameter, soft, fluctuant, subcutaneous mass
caudomedial to the left parietal horn. A fine
needle aspirate of the mass was obtained under
chute-restraint. Cytologic analysis revealed pe-
ripheral blood and a presumptive diagnosis of
hematoma was made.
One month after initial presentation, the
giraffe had intermittent bouts of inappetence,
lethargy, and abnormal neck posture. The mass
remained unchanged. A repeat fine needle
aspirate was obtained. Cytology revealed many
clusters of round cells with a moderate amount of
granular cytoplasm suggestive of poorly differ-
entiated sarcoma. Using behavioral restraint,
phlebotomy was performed for hematologic and
serum biochemical evaluation. Complete blood
count and serum chemistry abnormalities includ-
ed mild hyperproteinemia (8.8 g/dl; reference
range 5.9–7.9 mg/dl) and mild hyperfibrinogen-
emia (400 mg/dl; reference range 0–315 mg/dl).
Over the next 6 days, no improvement was seen.
Biopsy of the mass was elected.
Standing sedation was performed using detomi-
dine hydrochloride (Dormosedan, Pfizer Animal
Health, New York, New York 10017, USA; 10 mg
i.m.) delivered by hand injection. Sedation was
antagonized with yohimbine (ZooPharm, Lara-
mie, Wyoming 82070, USA; 66 mg i.m. [cumula-
tive]). Analgesic treatment was achieved with
ketoprofen (Ketofen, Fort Dodge Animal Health,
Fort Dodge, Iowa 50501, USA; 300 mg i.m.).
The soft tissue mass contained a soft, fluctuant
region cranially delimited by firm tissue. Two 4-
From the Smithsonian Institution’s National Zoo-
logical Park, 3001 Connecticut Avenue NW, Washing-
ton, D.C. 20008-2598, USA (Woc-Colburn, Murray,
Boedeker, Viner, Barthel, Sanchez); the Department of
Veterinary Pathology, Armed Forces Institute of
Pathology, 6825 16th Street NW, Washington, D.C.
20306, USA (Fleetwood); and the Children’s National
Medical Center, 111 Michigan Avenue NW, Washing-
ton, D.C. 20010-2970, USA (Newman). Present address
(Sanchez): Chicago Zoological Society, Brookfield Zoo,
3300 Golf Road, Brookfield, Illinois 60513, USA.
Correspondence should be directed to Dr. Woc-Colburn
( The author(s) prepared
this manuscript as part of their official duties with the
U.S. Government and are unable to assign rights to the
American Association of Zoo Veterinarians.
Journal of Zoo and Wildlife Medicine 41(4): 717–720, 2010
mm punch biopsies were obtained from the firm
aspect of the mass. Cytology of a Wright’s-
stained impression revealed a monomorphic
population of round cells with scant cytoplasm.
The biopsy sample was fixed in 10%neutral
buffered formalin and processed routinely for
histology. Histopathology revealed packets of
polygonal cells with indistinct cell borders, small
amounts of fibrillar cytoplasm, and up to five
irregularly round nuclei per cell with finely-
stippled chromatin and variably distinct nucleoli.
Packets of neoplastic cells were supported by a
fibrovascular stroma. The cells often lined the
boundaries of the packets, and cells at the center
of the packets were vacuolated or had lost cell
contact (Fig. 1). The mitotic activity was ap-
proximately 1 per 3400 field. In some areas,
neoplastic cells were more anaplastic; with a loss
of packeting arrangement, more abundant eosin-
ophilic cytoplasm, anisokaryosis, anisocytosis,
and large nucleoli. Immunohistochemical stain-
ing was performed on deparaffinized sections
using the avidin-biotin-peroxidase complex tech-
nique for vimentin (mouse monoclonal antibody,
clone V9, Ventana, Tucson, Arizona 85755,
USA; premixed solution), neuron-specific enolase
(mouse monoclonal antibody, clone E27, Ven-
tana; premixed solution), glial fibrillary acidic
protein (rabbit polyclonal antibody, Dako, Car-
pinteria, California 93013, USA; 1:16,000 dilu-
tion), Melan A (mouse monoclonal antibody,
clone A103, Novocastra, Newcastle NE12 8EW,
United Kingdom; 1:50 dilution), chromogranin
(rabbit polyclonal antibody, Dako; 1:1,600 dilu-
tion), synaptophysin (rabbit polyclonal antibody,
Ventana; premixed solution), muscle-specific ac-
tin (mouse monoclonal antibody, clone HUC1-1,
Ventana; premixed solution), myogenin (mouse
monoclonal antibody, clone F5D, Dako; 1:50
dilution), and myoD1 (mouse monoclonal anti-
body, clone 5.8A, Novocastra;1:50 dilution).
Sections were also stained under identical condi-
tions, with normal rabbit or normal mouse serum,
to serve as negative controls. These immunohis-
tochemical stains were incubated with diamino-
benzidine chromogen (Ventana) and counter-
stained with Mayer hematoxylin.
Strong positivity for actin and desmin was
found in the cytoplasm of approximately 50%of
the neoplastic cells, and nuclei were positive for
myogenin (100%of cells) and myoD1 (75%of
cells). Nearly 100%of the neoplastic cells were
also nonspecifically positive for vimentin in
the cytoplasm, as well as for S-100 protein
within nuclei. These immunohistochemical find-
ings, coupled with the histomorphology of the
mass, indicated embryonal rhabdomyosarco-
Surgical excision of the mass, followed by
intralesional chemotherapy under general anes-
thesia, was performed. The giraffe was immobi-
lized with medetomidine hydrochloride (Zoo-
Pharm; 6 mg), ketamine hydrochloride (Zoo-
Pharm; 400 mg) and A3080 (ZooPharm; 3 mg)
i.m. via hand injection. Muscle relaxation was
maintained with guaifenesin (Vedco, St. Joseph,
Missouri 64503, USA; 12,500 mg i.v. continuous
drip). Anesthesia was antagonized with naltrex-
one (ZooPharm; 50 mg i.m.) and atipamezole
(30 mg i.v. and 30 mg i.m.).
Right and left oblique skull radiographs
revealed lytic changes of the parietal bone
underlying the soft tissue mass. To control
intracranial swelling, dexamethasone (VetOne,
Meridian, Idaho 83680, USA; 500 mg i.v.) and
prednisolone sodium succinate (Solu-delta-cortef,
Pfizer Animal Health; 1,000 mg i.m.) were
The soft tissue mass located caudal to the left
parietal horn measured 10 310 36 cm. Wide
lateral surgical margins were obtained. On the
basilar aspect, the mass extended to the parietal
bone and full surgical excision was not possible.
Intralesional chemotherapy with 5-fluorouracil
(Fluoroplex, Allergan Inc., Irvine, California
92612, USA; 300 mg) was given. Histopathology
revealed that neoplastic cells extended to all cut
borders of the tissue submitted.
Over the next 11 days, the giraffe was treated
supportively. Five days postoperatively, a new
Figure 1. Embryonal rhabdomyosarcoma of a
Rothschild’s giraffe. Neoplastic polygonal cells are
arranged in packets or sheets. Mitotic figures are
present at a rate of approximately 1 per 3400 field.
H&E, 3200.
mass 2 34 cm developed at the incision site.
Eleven days after surgery, the giraffe became
ataxic, obtunded, and developed bilateral hori-
zontal nystagmus. Brief improvement of vestib-
ular signs was seen with diphenhydramine
(Benadryl, Baxter Healthcare, Deerfield, Illinois
60015, USA; 500 mg i.m.) administration.
Euthanasia was elected due to a grave prognosis.
On gross necropsy, a poorly healed incision site
with an 8 3834 cm hematoma subadjacent to
the incision was noted between the left parietal
horn and pinna. Below the hematoma, there was
a10310 34 cm irregular, soft, pale tan mass
infiltrating the adjacent skeletal muscle, salivary
gland, and bone. There was a 4 34cmareaof
complete bone loss in the base of the parietal
horn and the adjacent parietal bone covering the
parietal sinus. The bone between the parietal
sinus and the brain, at the level of the left cerebral
cortex and cerebellar hemisphere, was completely
lost. The tumor filled the sinus between the areas
of bone loss, compressed the left side of the
cerebellum, and was attached to the meninges of
the caudal left cerebral hemisphere (Fig. 2). The
caudal left cerebral cortex was malacic. There
were multifocal, large hemorrhages in the caudal
left cerebral cortex, the dorsal surface of the
brainstem, and between the left side of the
brainstem and the ventral aspect of the cerebel-
lum. Enlargement of the left mandibular lymph
node, due to tumor metastasis, was present.
There were numerous firm, tan nodules that were
up to 2 cm in diameter throughout the lung.
Tissues were fixed in 10%neutral buffered
formalin, processed routinely, and stained with
hematoxylin and eosin (H&E). Histopathology
revealed that the neoplasm previously described
had eroded the skull and caused extensive
malacia and gliosis of the adjacent gray and
white matter. Neoplastic cells focally infiltrated
the meninges. Tumor cells had also embolized to
the spinal cord vasculature in the area of C1–2.
Based on the histopathology and immunohisto-
chemistry, a diagnosis of embryonal rhabdomyo-
sarcoma with metastasis to the lung, mandibular,
and tracheobronchial lymph nodes was made.
In humans, embryonal rhabdomyosarcomas
are the second most-common malignant head
and neck tumor (18%) in the pediatric popula-
Those found along the parameningeal sites
have a poor prognosis, as 35%of the patients
develop metastases into the meninges and the
central nervous system.
In contrast, very few
embryonal rhabdomyosarcomas have been re-
ported along the head and neck of animals.
Several of these have been reported to affect
parameningeal sites such as the paranasal sinus,
nasal cavity, and infratemporal fossae, with
metastases to the meninges.
This giraffe’s
tumor may have originated in the parameningeal
region. Similar to other parameningeal rhabdo-
myosarcomas, it could have spread to the
meninges and surrounding skeletal muscle.
In both humans and domestic animals, treat-
ment of choice is wide surgical excision of tumor
followed by radiation or chemotherapy.
five-fluorouracil, a pyrimidine antagonist, has
been used in some protocols with varying
However, survival rates of patients with
embryonal rhabdomyosarcoma, even with che-
motherapy, rapidly decrease with the presence of
Areas of necrosis that involved large
swaths of neoplastic cells with enmeshed blood
vessels were observed on histopathology of the
tumor. This could indicate that intralesional
chemotherapy had a limited effect on tumor
Few spontaneous tumors have been reported in
giraffes. These include a pelvic chondrosarcoma
and a teratoma of the umbilical cord.
At the
National Zoological Park, a thyroid adenoma
and uterine leiomyoma have also been observed
(unpubl. data). None of these have been reported
to cause neurologic signs.
Acknowledgments: The authors would like to
thank the pathologists and technicians at the
Armed Forces Institute of Pathology who per-
formed the immunohistochemical stains. In
Figure 2. Brain from a 3-yr-old Rothschild’s gi-
raffe. The embryonal rhabdomyosarcoma that extended
through lysed calvarial bone and sinus distorts and
displaces the cerebellum and adjacent cerebrum. Bar 5
addition, the authors would like to thank Drs.
Mitch Bush and Scott Citino for their assistance
with the giraffe’s immobilization.
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Received for publication 26 September 2009
... To the best of our knowledge, osseous cyst-like in both medial femoral condyles [21], embryonal rhabdomyosarcoma [22], subependymal glioneuronal hamartoma in the mesencephalic aqueduct [23], pelvic chondrosarcoma [24], skin papillomas [25], teratoma of the umbilical cord [26], and giant verrucous carcinoma [27] have been reported in giraffes. This is the first report of congenital goiter with areas of SRC differentiation in a giraffe. ...
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Background Congenital goiter is a common thyroid metabolic disorder characterized by low levels of thyroid hormone, subsequent secretion of excess thyroid-stimulating hormone (TSH) from the pituitary gland, and compensatory hyperplasia of the glands. The presence of signet ring cells (SRCs) does not provide sufficient evidence for the diagnosis of a thyroid tumor, making histopathological diagnosis challenging. In addition, SRCs can also appear in congenital goiter. Therefore, a comprehensive diagnosis of congenital goiter is warranted based on clinical symptoms, autopsy, histopathology, and laboratory examination. Case presentation A juvenile giraffe at the Ordos Zoo in Ordos presented with symptoms of loss of appetite, serious salivation, and slow growth rate since birth. Its height and weight were significantly lower than those of other giraffes of the same age. The animal ultimately died at 17 months of age. Autopsy revelaed that the thyroids were hard, with an uneven surface and with the presence of many small raised follicles, and dense in cross-section. Other organs were visibly atrophic. Histopathologically, diffuse follicles were irregular in size and shape in the hyperplastic goiter. Some follicles were collapsed due to lack of colloids. The follicles were lined by single or multiple layers of hyperplastic follicular cells (HFCs), some of which were exfoliated in the lumen. The HFCs were either cuboidal with eosinophilic cytoplasm and many red small granules or showed SRC differentiation, with nuclei pressed to one edge of the cell and distorted by cytoplasmic mucin that appeared as a single clear vacuole HFCs and as a foamy, multivesicular cytoplasmic material in others. Scattered necrosis of myocardial cells and hepatocytes, cerebral hemorrhage, necrosis of intestinal villi, and obvious atrophy of organs were also observed. Immunohistochemical tests were strongly positive for thyroglobulin and thyroid transcription factor-1 (TTF-1) in the cytoplasm of HFCs. Conclusions Here we present a case of congenital goiter with areas of SRC differentiation in the thyroid of a juvenile giraffe.
A 4‐year‐old, male Rothschild's giraffe presented with a rapidly growing, hemispherical, approximately 40 × 20 × 20 mm, raised, firm mass located on the mid‐region of the left lateral thigh. Complete surgical excision (minimal 20 mm margins in all orientations) was achieved under behavioural restraint and local anaesthesia. Cytology and histopathology diagnosed a poorly differentiated malignant mesenchymal neoplasm, with nuclear karyomegaly, multinucleation and atypical horseshoe‐like forms. The neoplastic cells exhibited diffuse strong cytoplasmic immunopositivity to vimentin, and were negative to smooth muscle actin, desmin, glial fibrillary acidic protein, and CD18 immunomarkers, giving a diagnosis of undifferentiated pleomorphic sarcoma. At 1 year follow‐up, the giraffe is clinically well with no health issues after complete excision, and no evidence of local recurrence or distant metastases, based on physical examination and routine haematology/biochemistry. To the authors’ knowledge, this is the first report of an undifferentiated pleomorphic sarcoma (atypical fibroxanthoma‐subtype) in a giraffe.
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Humans are not the only species to spontaneously develop metastatic cancer as cases of metastasis have been reported in a wide range of animals, including dinosaurs. Mouse models have been an invaluable tool in experimental and clinical metastasis research, with the use of genetically-engineered mouse models that spontaneously develop metastasis or ectopic/orthotopic transplantation of tumour cells to wildtype or immunodeficient mice being responsible for many key advances in our understanding of metastasis. However, are there other species that can also be relevant models? Similarities to humans in terms of environmental exposures, life-span, genetics, histopathology and available therapeutics are all factors that can be considered when looking at species other than the laboratory mouse. This review will explore the occurrence of metastasis in multiple species from a variety of domestic, captive and free-living veterinary cases to assist in identifying potential alternative experimental and clinical research models relevant to humans.
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Differentiation therapy provides an alternative treatment of cancer that overcomes the undesirable effects of classical chemotherapy, i.e. cytotoxicity and resistance to drugs. This new approach to cancer therapy focuses on the development of specific agents designed to selectively engage the process of terminal differentiation, leading to the elimination of tumorigenic cells and recovery of normal cell homeostasis. A series of new anti-cancer pyrimidine acyclonucleoside-like compounds were designed and synthesized by structural modifications of 5-fluorouracil, a drug which causes considerable cell toxicity and morbidity, and we evaluated their applicability for differentiation therapy in human rhabdomyosarcoma cells. We tested the pyrimidine derivative GR-891, (RS)-1-[[3-(2-hydroxyethoxy)-1-isopropoxy]propyl]-5-fluorouracil, an active drug which shows low toxicity in vivo and releases acrolein which is an aldehyde with anti-tumour activity. Both GR-891 and 5-fluorouracil caused time- and dose-dependent growth inhibition in vitro; however, GR-891 showed no cytotoxicity at low doses (22.5 micromol l(-1) and 45 micromol l(-1)) and induced terminal myogenic differentiation in RD cells (a rhabdomyosarcoma cell line) treated for 6 days. Changes in morphological features and in protein organization indicated re-entry in the pathway of muscular maturation. Moreover, GR-891 increased adhesion capability mediated by the expression of fibronectin, and did not induce overexpression of P-glycoprotein, the mdr1 gene product, implicated in multidrug resistance. New acyclonucleoside-like compounds such as GR-891 have important potential advantages over 5-fluorouracil because of their lower toxicity and their ability to induce myogenic differentiation in rhabdomyosarcoma cells. Our results suggest that this drug may be useful for differentiation therapy in this type of tumour.
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A 7-year-old, female, domestic medium-haired cat had a recurrent deep dermal mass in the interscapular region after initial surgical removal 3 months earlier. The cat had received a killed rabies vaccine and a five-in-one vaccine in the same area about 2 months prior to the first surgery. The relapsed mass was diagnosed as vaccine-associated sarcoma. The cat was euthanized 2 months later because of hind limb paralysis. At necropsy, multiple, poorly demarcated, nodular masses were seen in the muscles around the shoulders, neck, and thoracic vertebrae. Pulmonary metastasis and spinal epidural invasion at T1-T3 with regional cord compression and malacia were observed. Microscopically, the masses consisted of interwoven bundles of spindle cells with prominent multinucleated giant cell formation. The neoplastic cells stained strongly positive for myoglobin, and moderately but variably positive for vimentin, desmin, and alpha- smooth muscle actin. Phosphotungstic acid-hematoxylin staining revealed cytoplasmic striations in scattered tumor cells. The tumor was considered a vaccine-associated rhabdomyosarcoma.
The immunohistochemical study of 60 cases of rhabdomyosarcomas made it possible to test eight different antibodies currently used in tumour pathology: i.e., antisera to vimentin, desmin, myoglobin, cytokeratin, epithelial membrane antigen, S100 protein, neurofilaments, and leukocyte common antigen. Vimentin was found in 58 cases (97 per cent), desmin in 49 cases (82 per cent), myoglobin in 23 cases (38 per cent), S100 protein in 7 cases (12 per cent), and cytokeratin in 3 cases (5 per cent). Other markers were negative. S100 protein was present in large round tumour cells with abundant eosinophilic cytoplasm (round rhabdomyoblasts), whereas cytokeratin was present in small tumour cells similar to those observed in rhabdoid sarcoma. This unexpected staining should become common knowledge for the correct interpretation of the immunohistochemical study of small cell tumours in the young.
Juvenile rhabdomyosarcomas were diagnosed in two young dogs based on the results of histopathology, phosphotungstic acid-hematoxylin stain, immunohistochemistry, and the age of the dogs. One dog, an 11-month-old Rottweiler, had tumor masses in the maxillary gingiva and the urinary bladder. Histologically, the gingival mass was an alveolar type of rhabdomyosarcoma and the urinary bladder mass was an embryonal type. The other dog, a 1.5-year-old Basset Hound, had an embryonal rhabdomyosarcoma involving the oropharynx and the temporal muscles, with metastasis to the regional lymph node and lungs.
A 23-month-old, male, Labrador retriever dog with a history of slowly progressive right-sided atrophy of the masticatory muscles was submitted for necropsy. A highly invasive neoplasm which destroyed adjacent soft tissues including the right trigeminal nerve was found in the right side of the cranial cavity. Metastases to the liver were also present. Microscopical features of the neoplasm were compatible with those of rhabdomyosarcoma, embryonal type. This diagnosis was confirmed by immunohistochemical demonstration of desmin and muscle actin within tumour cells. In human patients, rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and adolescence. Parameningeal rhabdomyosarcomas are well-known topographic variants that are often non-amenable to complete surgical resection and therefore carry a more guarded prognosis. Juvenile parameningeal rhabdomyosarcoma resulting in denervation atrophy of the muscles of mastication has not been reported previously in dogs. Rhabdomyosarcoma should be included in the differential diagnosis of neoplastic conditions in the head and neck region of juvenile dogs presented with cranial nerve palsies or other neurological deficits suggestive of meningeal or central nervous system invasion.
A 10-year-old terrier crossbreed presented with a change in bark intonation of 3-4 month's duration and pronounced panting. Four variably sized masses were observed within the oral cavity. The largest mass was located within the parenchyma at the caudal region of the tongue. Others were located on the left arytenoid, within the soft palate, and in the oropharynx above the soft palate. Histopathologic specimens consisted of large round to polygonal cells occasionally containing multiple nuclei and rare faint cytoplasmic cross striations. Staining was weakly positive with periodic acid-Schiff. Immunocytochemistry was strongly diffusely positive for muscle-specific actin, myoglobin, and desmin and scattered positive for S-100 and vimentin. Phosphotungstic acid-hematoxylin staining enhanced cytoplasmic cross striations. The cytoplasm of all neoplastic cells was filled with mitochondria on electron microscopy. The final diagnosis was multifocal/metastatic rhabdomyosarcoma.
A 10-year-old, female, mongrel showed hemorrhage from vulva. By magnetic resonance image (MRI) and endoscopic examination, a multipapillary mass with a grape-like appearance was found around the urethral opening. Histologically, the mass consisted of variable-sized round-, spindle-to-polygonal-shaped tumor cells including many multinuclear cells. Mitotic figures were also frequently observed. In some areas, that tumor cells were loosely arranged, with intercellular myxoid components. Immunohistochemically, these tumor cells were strongly positive for vimentin and focally positive for desmin but negative for myoglobin. Thus, the case was diagnosed as a relatively poorly differentiated botryoid rhabdomyosarcoma by the macroscopic, histopathologic, and immunohistochemical identification. This is the first report of botryoid rhabdomyosarcoma developing in the vagina of a dog.
Rhabdomyosarcomas comprise a relatively common diagnostic entity among childhood cancers and a relatively rare one among adult tumors. They may possess a variety of histologies that generally differ among age groups. These lesions appear to be separate biologic entities as well as morphologic categories, with embryonal tumors having genetic lesions related to loss of heterozygosity and aberrant parental imprinting, alveolar tumors containing genetic fusions between PAX and forkhead genes, and pleomorphic tumors showing an accumulation of genetic lesions similar to other adult high-grade sarcomas. To present guidelines for diagnosis of rhabdomyosarcoma and recent finding concerning the biology and classification of these lesions. Review of recent and older published literature and distillation of the authors' experience. Infants and young children tend to have embryonal rhabdomyosarcomas, adolescents and young adults tend to have alveolar rhabdomyosarcomas, and older adults tend to have pleomorphic rhabdomyosarcomas, although there is some overlap. Newer rare entities, including spindle cell rhabdomyosarcoma and sclerosing rhabdomyosarcoma, have been described in children and adults. Fusion-positive tumors have a distinct molecular signature with downstream activation of a number of myogenic and tumorigenic factors. Genetic testing may be successfully used for diagnosis and may guide therapy in future clinical trials. Differential diagnosis has become simpler than in previous years, because of use of myogenic factors in immunohistochemistry, but classification based solely on histologic features remains challenging.