Rhabdomyosarcoma of the head and neck in children

The purpose of this study was to determine the rhabdomyosarcoma types involving the head and neck (H&N) region in children and their immunophenotype.

Anatomic pathology archives at Texas Children's Hospital were searched for all rhabdomyosarcoma cases over a 20-year period. One-hundred and thirty-seven cases were identified, with 50 being H&N cases. The cases were typed according to the Intergroup Rhabdomyosarcoma Study (IRS) criteria. Immunocytochemistry for myogenic and non-myogenic markers was performed on all H&N cases. Electron micrographs from cases (n=32) where ultrastructural examination had been performed at the time of original diagnosis were reviewed.

Children with H&N rhabdomyosarcomas had a mean age of 5.3 years (median 4 years). There was a male predilection (1.7M:1.0F). Primary tumor sites were: face NOS (18%), orbit/periorbital (16%), nasal cavity/nose (14%), lymph nodes (12%), paranasal sinuses (10%), parameningeal (10%), parotid gland (6%), neck (6%), infratemporal fossa/zygoma (2%), buccal mucosa (2%), palate (2%), and larynx (2%). Metastatic disease at diagnosis (33% of all cases) occurred in the bone marrow (11%), cerebrospinal fluid (6%), peritoneal fluid (6%), lung (4%), parietal pleura (2%), pleural fluid (2%) and pericardial fluid (2%). Rhabdomyosarcoma types (IRS criteria) were: embryonal (60%), alveolar (classic and solid subtypes, 28%), botryoid (4%), undifferentiated (4%), spindle cell (2%) and anaplastic (2%). Immunocytochemical findings were: polyclonal desmin (96%); myogenin (96%); muscle-specific actin (74%), smooth muscle actin (12%). Nonmyogenic markers included: vimentin (100%), CD99 (16%), p53 (16%), pancytokeratin (10%), NSE (8%), LCA (6%), CD20 (6%), EMA (2%), and NB-84 (0%, neuroblastoma). Undifferentiated sarcoma expressed only vimentin. By ultrastructural examination, 44% had readily identified z-bands and myofilaments, 37% had infrequent to rare myofilaments and z-bands, and 19% had myotubular intermediate filaments.

Distribution of H&N rhabdomyosarcoma IRS types is similar to that for all primary sites, with the exception that embryonal types are modestly increased while alveolar type is mildly decreased. There are many non-myogenic immunocytochemical markers that cross-react with rhabdomyosarcoma. Differentiation between favorable and unfavorable rhabdomyosarcoma types is important for appropriate therapy, and predicting prognosis and survival.