Man in his 60s with a bladder mass   


Rhabdomyosarcoma of the bladder (RMS), alveolar pattern

Bladder rhabdomyosarcoma (RMS) with an alveolar pattern is extremely rare. It constitutes less than 0.5% of all bladder tumors and is often found in children 2-6 years of age. 25% to 30% have metastases at the time of primary diagnosis, most commonly affecting the bone marrow and distal nodes. ARMS has a poorer overall prognosis than the embryonal subtype. Staging is predictive of outcome. Common variables that affect survival are anaplastic features, tumor site and size, distal lymph node involvement, and distant metastases. Microscopically, tumor cells are often small with scant cytoplasm. Nuclei are round with dull chromatin. The tumor has two main subtypes: classic and solid. Occasional rhabdomyoblasts, coagulative tumor cell necrosis, and anaplastic cellular features may be seen. The tumor is positive for myogenin, desmin, muscle-specific actin, and MyoD1. The tumor treatment modality is complete excision. The differential diagnosis includes alveolar soft part sarcoma, embryonal rhabdomyosarcoma, Merkel cell carcinoma, and metastatic neuroendocrine carcinoma. Both Merkel cell carcinoma and metastatic neuroendocrine carcinoma lack gene fusion.


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