Answer: Metastatic prostatic adenocarcinoma

Histology: This is a high grade neoplasm featuring cells with high nucleus to cytoplasm ratios, prominent mitoses, and extensive necrosis. Remnants of lymph node are evident at the periphery of the lesion, indicating that this lesion represents an obliterated lymph node. The tumor cells have fairly uniform, round nuclei, with relatively prominant single nucleoli. Tumor cells are immunoreactive for cytokeratin but not for leukocyte common antigen (CD45), CD20, CD43, or CD79a, diagnostic of carcinoma and excluding lymphoma. The tumor was non-reactive for cytokeratin 903, but did label for prostate specific antigen (PSA) and P501S, consistent with metastatic prostatic adenocarcinoma.

Further work-up revealed a bladder mass within this patient, which cystoscopically appeared to be a tumor invading the bladder wall from the exterior. This seems likely to have been an undiagnosed prostatic adenocarcinoma.

Discussion: Burkitt lymphoma features highly proliferative lymphoid cells with intermediate, squared-off nuclei. The labeling for cytokeratin and absence of reactivity for lymphoid markers excludes this diagnosis, which was favored clinically. Small cell carcinoma should feature cells with hyperchromatic nuclei, non-prominent nucleoli, and nuclear molding. Pulmonary adenocarcinoma would be more pleomorphic than the current case, and often labels with TTF-1.

Prostatic adenocarcinoma is amenable to relatively non-toxic endocrine therapy when it presents with metastatic disease. Hence, in the setting of disseminated metastatic adenocarcinoma in a male, prostatic origin is worth excluding so as not to deny a patient a relatively non-toxic treatment.