Primary and metaplastic choriocarcinoma of the bladder. A report of two cases.

Two cases of primary choriocarcinoma arose in the urinary bladder in males aged 72 and 70 years. Human chorionic gonadotropin (hCG) in serum and urine was significantly elevated in both cases. Cytologic features consisted of bizarre mononucleate and multinucleate giant cells with numerous erythrocytes, necrotic cells and neutrophils, indicating the possibility of choriocarcinoma. Histologically, one tumor consisted of an admixture of choriocarcinomatous areas and transitional cell carcinoma (TCC) with or without syncytiotrophoblastic differentiation, and the other was composed of pure choriocarcinoma. Immunohistochemical examination revealed that syncytiotrophoblasts and a small number of TCC cells were intensely positive for hCG in their cytoplasm. The histogenesis of choriocarcinoma arising in the bladder is considered to be metaplasia or retro-differentiation from TCC to trophoblasts because of TCC's differentiating to hCG-positive trophoblasts, as seen in one of the present cases.