Cardiac embryonal rhabdomyosarcoma in a domestic shorthair cat

Rhabdomyosarcomas (RBMs) are rare neoplasms arising from striated muscle tissues in domestic animals and are exceptionally uncommon, affecting the heart of domestic cats. A case of cardiac embryonal RBM was detected in a two-year-old female domestic shorthair cat. The cat exhibited dyspnea, anorexia, pericardial and pleural effusions, ultimately succumbing to severe respiratory arrest. Gross post-mortem examination revealed a firm yellow-tan mass measuring 2.5 × 1.5 cm protruding from the right atrium, along with metastatic nodules of various sizes dispersed throughout the liver, spleen, and lungs. On histology, the right atrium exhibited a highly cellular infiltrative and vascularized mass predominantly composed of spindle and small round cells arranged in dense cellular bundles supported by a scant fibrous stroma interspersed with scarce regions of loosely myxoid stroma. Comparable histological features were noted in the metastatic lesions. Immunohistochemical analysis revealed positive immunolabeling for vimentin, desmin, MyoD1, and fast myosin, while no immunostaining was observed for smooth muscle actin, chromogranin, and S100. Histological and immunohistochemical features supported the diagnosis of metastatic cardiac embryonal RBM spindle cell variant in the cat. Cardiac embryonal RBMs should be included in the differential diagnosis of cardiac and thoracic neoplasms in domestic cats presenting with clinical signs indicative of cardiac arrest or sudden death.

Disseminated pleomorphic rhabdomyosarcoma in a horse

An 8-y-old National Show Horse mare was presented for evaluation of pneumonia and laminitis. Harsh bronchovesicular sounds were auscultated throughout both lung fields, and the mare had signs of moderately painful laminitis. Thoracic ultrasonography revealed lung consolidation throughout the dorsal aspect of both lungs, and radiography revealed an extensive diffuse-to-patchy bronchointerstitial lung pattern. The mare's clinical condition rapidly deteriorated, and euthanasia was elected. On postmortem examination, the lungs, omentum, spleen, liver, adrenal glands, kidneys, and femur contained 0.5-2.5-cm, firm, tan nodules. Histologically, the lungs, spleen, liver, kidneys, adrenal glands, omentum, left eye, and femur were infiltrated by bundles and nests of pleomorphic polygonal-to-spindloid cells intermixed with frequent multinucleate cells. Lymphatic vessels in the affected tissues were frequently distended with tumor emboli. Neoplastic cells were diffusely positive for vimentin, desmin, sarcomeric actin, myoblastic differentiation protein 1, and myogenin, supportive of the diagnosis of rhabdomyosarcoma (RMS), which is a rare neoplasm in horses. Cross-striations were not evident with H&E or phosphotungstic acid-hematoxylin stains. Markedly pleomorphic neoplastic cells, multinucleate cells, and lack of cross-striations suggested the subclassification of pleomorphic RMS.

Biological behaviour and ezrin expression in canine rhabdomyosarcomas: 25 cases (1990-2012)

There are few published reports of canine rhabdomyosarcomas. In human paediatrics, rhabdomyosarcomas account for 5%-10% of all tumours and >50% of soft tissue sarcomas. They have an aggressive biologic behaviour; most patients develop diffuse metastatic disease. Ezrin, a cytoskeleton linker protein, has been correlated with metastasis in a number of tumours, including rhabdomyosarcomas. The goal of this study was to describe dogs with non-urinary rhabdomyosarcomas including clinical findings, ezrin expression and outcome. Twenty-five dogs with rhabdomyosarcomas were identified from two institutions' databases. Signalment, primary tumour location, cytologic and histologic findings, metastatic sites, treatments, survival time and necropsy results were recorded. Immunohistochemical staining for ezrin expression was performed on archived samples; cellular localization of ezrin was characterized. The mean and median age of all patients was 4.3 and 2 years, respectively. Subcutaneous and retrobulbar/orbital were the most common primary tumour locations. Sixteen dogs had metastatic disease at diagnosis. Three dogs presented with diffuse disease where a primary tumour could not be identified. A round cell tumour was the initial diagnosis in 32% of cases, and 76% of cases required immunohistochemistry to establish the diagnosis. The median survival was 10 days. Twenty-one cases had archived samples available for ezrin staining; all but one was positive and exhibited both membranous and cytoplasmic localization. Rhabdomyosarcomas occur in young dogs, may have a round cell appearance, and exhibit aggressive biologic behaviour. Given ezrin's defined role in metastasis, its observed expression in the tumours in this study suggest its possible role in canine rhabdomyosarcoma's aggressive biologic behaviour.

Diagnosis and Multimodal Treatment of Metastatic Maxillofacial Juvenile Embryonal Rhabdomyosarcoma in a Young Golden Retriever

A 2 yr old male castrated golden retriever was evaluated for a rapidly progressing maxillofacial spindle cell tumor. On examination, an ill-defined left maxillary mass, a 2 cm swelling under the left eye, and an enlarged left mandibular lymph node were noted. The dog was bright and alert but appeared painful upon jaw extension. Cytology from the lymph node revealed metastatic disease. Thoracic radiographs and computed tomography scan revealed pulmonary nodules. Computed tomography of the head and neck revealed a 6.7 × 4.1 × 6.5 cm mass at the rostral aspect of the left zygomatic arch invading the orbit. A second opinion of the biopsy specimen in conjunction with positive immunohistochemical staining for desmin led to a revised diagnosis of rhabdomyosarcoma. Treatment consisted of three doses of palliative radiation therapy, in 8 Gy fractions, and chemotherapy with vincristine, cyclophosphamide, and doxorubicin. A rapid clinical response was noted shortly after treatment initiation; however, the response was temporary, and the dog was euthanized due to widespread metastatic disease and associated clinical signs 74 days after initial therapy. This is one of the first reports describing positive results from multimodal treatment with chemotherapy and radiation therapy of a maxillofacial juvenile rhabdomyosarcoma in the veterinary literature.

Canine orbital rhabdomyosarcoma: a report of 18 cases

PURPOSE

To describe clinical and pathological features of canine orbital rhabdomyosarcoma (COR).

METHODS

Retrospective review of patients with COR from the archives of the Comparative Ocular Pathology Laboratory of Wisconsin and the University of Wisconsin Veterinary Medical Teaching Hospital (1983-2014).

RESULTS

Eighteen cases of COR were identified, all diagnosed in an 8-year period (2006-2014). Affected dogs were typically young (range 1-8; median 2 years), and both sexes were equally represented. Common clinical signs included exophthalmos (16/18) with dorsolateral deviation of the globe (10/18) and elevation of the nictitans (12/18). Ultrasonography, performed in nine cases, revealed an orbital mass with mixed echogenicity and posterior globe indentation. Advanced imaging, performed in nine cases, demonstrated a soft tissue mass with variable contrast enhancement and lysis of the orbital bones (5/9). Histologically, all tumors were subclassified as embryonal rhabdomyosarcoma. All neoplasms demonstrated positive immunohistochemical labeling for desmin, and 14/18 were positive for skeletal muscle actin. Follow-up information was available for 15/18 cases. Older dogs, aged 6-8 years, had no clinical signs of recurrence or metastasis 8-13 months postdiagnosis (4/4). Most younger dogs (9/11), aged 1-4 years, were euthanized within 6 months (median 2.5 months) of diagnosis due to recurrence at the surgical site (5/9) and/or metastasis (5/9).

CONCLUSIONS

Canine orbital rhabdomyosarcoma is a highly malignant neoplasm in juvenile dogs, but may be amenable to surgical resection in older dogs. This duality in biologic behavior may reflect differences in tissue of origin between juvenile onset tumors and adult onset tumors.

A Comparative Review of Canine and Human Rhabdomyosarcoma With Emphasis on Classification and Pathogenesis

Rhabdomyosarcomas are a diverse group of malignant mesenchymal neoplasms exhibiting variable levels of differentiation toward skeletal myocytes. Neoplastic cells may resemble relatively undifferentiated myoblasts, satellite cells, or more differentiated elongated spindle cells and multicellular myotubes. In veterinary medicine, classification into subtypes and variants is based on an outdated system derived from human pathology and is solely based on histologic characteristics. In contrast, classification of human rhabdomyosarcoma is based on histologic, immunohistochemical, and molecular diagnostic techniques, and subclassification has clinical and prognostic relevance. Relevance of tumor subtyping has not been established in veterinary medicine. Recent discoveries of components of the molecular pathogenesis and genomes of human rhabdomyosarcomas have led to new diagnostic techniques and revisions of the human classification system. The current classification system in veterinary medicine is reviewed in light of these changes. Diagnosis of rhabdomyosarcoma using histopathology, electron microscopy, and the clinical aspects of human and canine rhabdomyosarcomas is compared. The clinical features and biologic behavior of canine rhabdomyosarcomas are compared with canine soft tissue sarcomas.

Embryonal rhabdomyosarcoma in a Rothschild's giraffe (Giraffa camelopardalis rothschildi)

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.

Poorly Differentiated Uterine or Cervical Sarcoma in a Young Dog

A 1.5 year old, female, spayed, Labrador retriever with a history of three abdominal surgeries within the previous two months presented to the North Carolina State University Veterinary Teaching Hospital for evaluation of a pelvic inlet mass causing fecal tenesmus, obstipation, and dysuria. Abdominal ultrasound revealed a caudal abdominal mass extending into the pelvic cavity. Cytologic evaluation of the mass showed a pleomorphic round to fusiform cell population with histiocytic and suppurative inflammation. The primary differential was neoplasia, but inflammation with cellular pleomorphism could not be excluded. Via histopathology and immunohistochemistry, a diagnosis of poorly differentiated sarcoma originating from the uterus or cervix with widespread intra-abdominal dissemination and metastasis was made. Sarcomas of any type are rare in young dogs with only sporadic cases of poorly or undifferentiated sarcomas reported. This case is a unique presentation of an aggressive, poorly differentiated sarcoma arising from the cervix or uterus in a young dog and illustrates the importance of histologic evaluation of surgically resected tissues that are abnormal in appearance.