Subcutaneous embryonal rhabdomyosarcoma in a dog: cytologic, immunocytochemical, histologic, and ultrastructural features

Abstract

A subcutaneous mass on the left antebrachium of an 11-year-old intact female English Pointer dog was evaluated presurgically by cytologic examination and immunocytochemical staining. The sample consisted of discrete, variably sized, markedly pleomorphic neoplastic cells that expressed vimentin with diffuse cytoplasmic staining, desmin with focal paranuclear staining, and myoglobin with diffuse cytoplasmic staining, consistent with a diagnosis of rhabdomyosarcoma. Lymphocytic and histiocytic markers were negative. Aspirates of the enlarged ipsilateral prescapular lymph node were positive for metastatic disease. Surgical excision of the tumor and lymph node were followed by histologic and electron microscopic examination. Histomorphologic appearance of neoplastic cells from the mass and the lymph node paralleled cytologic findings; the histologic diagnosis was round cell variant of embryonal rhabdomyosarcoma. By ultrastructural evaluation, cells contained numerous mitochondria and masses of cytoplasmic tangled myofilaments, features typical of rhabdomyoblasts. The dog received doxorubicin (30 mg/m(2) ) every 3 weeks for 5 treatments. Local recurrence developed 6 months after resection but was not treated. Despite a guarded prognosis and untreated local recurrence, the dog was still alive 18 months after surgery. Cytologic evaluation and immunocytochemical staining were pivotal for the presurgical diagnosis of rhabdomyosarcoma.

What is your diagnosis? Fine‐needle aspirate from a nasal mass in a dog

“…The round cell variant of embryonal rhabdomyosarcoma was considered due to the large cellular diameters. However, the scant cytoplasm made this diagnosis less likely, as cytologic features typical of rhabdomyoblasts, including abundant basophilic cytoplasm, and frequent paranuclear clear halos, were absent in the present case. Cellular cannibalism, occasionally observed in this neoplasm (Figure B), has been suggested as a diagnostic marker of malignancy, although it is not specific for NEC …”

What is your diagnosis? Dermal mass over the ribs with metastasis to lymph nodes in a dog

“…Extensive metastases of rhabdomyosarcomas originating in the urinary bladder have been reported; however, additional imaging was not performed on this patient to confirm or rule out this possibility. A subcutaneous embryonal rhabdomyosarcoma has been reported with metastasis to a lymph node, and metastasis to the lymph node from the dermal mass was considered to be most likely in this case.…”

The use, publication and future directions of immunocytochemistry in veterinary medicine: a consensus of the Oncology‐Pathology Working Group

“…Allows for the use of antibodies that are not effective in formalin fixed tissue, for example, T‐cell subsets Can offer rapid pre‐surgical diagnosis to aid in surgical planning and chemotherapeutic protocols Unlike flow cytometry, ICC allows assessment of cell morphology and direct visualization of the cell population of interest and its immunoreactivity.…”

“…A common mistake in the application of ICC is ordering too few stains, which either produces bias towards the favoured diagnosis or results in the lack of a definitive diagnosis. The importance of this was stressed by Fowler et al in a review of ICC in human medicine and was demonstrated in a case report of rhabdomyosarcoma in a dog . In this case report, the authors proposed a list of differential diagnoses which included rhabdomyosarcoma along with a tumour of histiocytic or plasma cell origin, based on cytological evaluation of a subcutaneous tumour.…”