Fine-needle aspiration of metastatic prostatic neuroendocrine carcinomas: cytomorphologic and immunophenotypic features.

Metastatic prostatic carcinoma may, in rare occasions, present as a neuroendocrine tumor. Its recognition is crucial to avert a wrongful exclusion of prostate as a primary site. We report five cases of metastatic prostatic neuroendocrine carcinoma diagnosed by image-guided fine-needle aspiration biopsy. The aspirate smears showed loosely cohesive or dyscohesive clusters of tumor cells with scanty (three cases) to moderate amount (two cases) of cytoplasm, speckled or coarse chromatin and inconspicuous nucleoli. Nuclear molding and necrosis were focally present in two cases. Immunohistochemically, the tumor cells were positive for synaptophysin or/and chromogranin, but negative for prostatic specific antigen and prostatic specific acid phosphatase. Review of prior prostate biopsies/resections revealed adenocarcinoma with focal neuroendocrine differentiation in all cases, with two cases being newly recognized on retrospective review. Confirming neuroendocrine differentiation in the prior biopsy/resection may help to establish a link between metastasis and prostate primary.