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

Abstract

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 In veterinary medicine, classification into subtypes and variants is based on an outdated system derived from human pathology and is solely based on histologic characteristics.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 Siberian chipmunk (Tamias sibiricus): a case report

“…RMSs are also considered the rarest naturally occurring tumours in rodents and have been primarily reported in laboratory rats and mice (Table 1). In contrast to reports describing the frequent occurrence of RMSs in younger dogs (commonly less than or equal to 2 years old) and children (Caserto 2013), based on the information of Merck Research Laboratories, older rats were considered to have a higher incidence of RMSs (an average age of 103 weeks; Conner 1994). However, the relationship to age is controversial, because there are more reported cases from younger rats and mice in recent times (commonly less than or equal to 1-year-old, the youngest was eight weeks old; Sundberg et al 1991;Conner 1994;Germann et al 1994;Radi 2006;Chang et al 2008) and A/J mice show a high frequency of RMSs in all age groups (Sher et al 2011).…”

“…Consequently, the neoplasm was diagnosed as a myotubular variant of embryonal RMS. (Caserto 2013). Desmin is expressed in skeletal, cardiac, smooth muscle cells and myofibroblasts.…”

“…Undifferentiated myoblast cells are expected to express less desmin and more myogenin; moreover, myogenin has been found to be expressed diffusely in human alveolar RMSs, which are poorly differentiated tumours. Conversely, only few cells in human embryonal RMSs express myogenin (Hostein et al 2004;Caserto 2013). Although the sub-classification of…”

“…In domestic animals, case reports of RMSs in dogs are more common than for any other species, followed by reports in cats, horses, sheep and pigs (Caserto 2013). RMSs are also considered the rarest naturally occurring tumours in rodents and have been primarily reported in laboratory rats and mice (Table 1).…”

Misdiagnosis of primary pleomorphic rhabdomyosarcoma of the right thigh in a young adult: A case report

“…In the present study, the patient was misdiagnosed with schwannoma, which led to the progression of the disease for half a year; therefore, fine-needle aspiration is crucial to the diagnosis of soft tissue masses. The histological manifestations of RMS widely vary, and the histopathological diagnosis is based on morphological, immunohistochemical and ultrastructural findings that reveal a skeletal muscle phenotype (16,17). PRMS is histologically distinguished from the two more common subtypes (embryonal and alveolar) by the haphazard arrangement of cells that are composed of large, pleomorphic nuclei and eosinophilic cytoplasms.…”