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Thanks to Dr. Carolina Martinez Ciarpaglini, University Clinic Hospital of Valencia (Spain), for contributing this case and the discussion and to Dr. Borislav Alexiev, Northwestern University, Chicago, Illinois (USA), for the Editorial Board review. To contribute a Case of the Month, follow the guidelines on our Case of the Month page.
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Case of the Week #276
An 11 year old boy presented with a left tonsillar mass present for three weeks. A biopsy was taken.
What is your diagnosis?
Diagnosis: Embryonal rhabdomyosarcoma
Embryonal rhabdomyosarcoma is a primitive soft tissue sarcoma with small blue cells resembling embryonic skeletal muscle. It is the most common rhabdomyosarcoma (RMS) subtype (65% of RMS cases), and usually occurs in children ages 3-10 years in the head and neck (sinonasal tract, oral cavities, orbit, ear, periorbital region and pharynx), prostate or paratesticular regions. Subtypes include embryonal-NOS, anaplastic and botryoid. Embryonal-NOS is the most common subtype (75%), usually affecting boys. It peaks at ages 0-4 years (US National Cancer Institute).
The tumor consists of dense zones of undifferentiated, differentiating and well differentiated cells. A cambium layer (cells immediately beneath the epithelium) ) may be present especially in the botryoid variant. Undifferentiated cells are blue cells with minimal wispy cytoplasm but no skeletal differentiation, and central nuclei. Differentiating cells have moderate amphophilic or eosinophilic cytoplasm, often fibrillar. They may have a tadpole shape, often with nuclei arranged in tandem (so called strap cells). Some differentiated cells may have cytoplasmic cross-striations.
Tumors cells, as in this case, are immunoreactive for actin, desmin, myogenin and myoD1. There may occasionally show aberrant immunoreactivity for S100 and CAM5.2. The differential diagnosis consists of other small blue cell tumors, such as lymphoma and neuroblastoma. All children with rhabdomyosarcoma require multimodality therapy with systemic chemotherapy and either surgery or radiation therapy. Overall 5 year survival is over 80%, although it is much less for those with metastatic disease (eMedicine).