Metastatic small-cell carcinoma of the prostate diagnosed by fine-needle aspiration biopsy.

Fourteen fine-needle aspiration biopsies (FNABs) of metastatic small-cell carcinoma done on 12 patients who had histologically documented primary small-cell carcinoma of the prostate are described. The FNABs were of lymph node (four cases), liver (four cases), bone (two cases), pancreas (one case), perirectal soft tissue (one case), perineum (one case), and lung (one case). One patient underwent three FNABs. No patient had a second primary tumor elsewhere. Cytologic smears were cellular with numerous single tumor cells, many apoptotic bodies, and variable numbers of mitotic figures. Tight cell clusters with molded nuclei and finely stippled chromatin were seen in all cases. An organoid pattern of tumor cells was seen focally in two cases. Features distinguishing small-cell carcinoma from poorly differentiated prostate carcinoma were cell size, finely stippled chromatin, inconspicuous nucleoli, and numerous single tumor cells. Distinction from small-cell carcinoma of other primary sites requires clinical and radiologic correlation. We conclude that cytologic specimens are useful for documenting metastatic small-cell carcinoma of the prostate and for differentiating between it and conventional prostate carcinoma in metastatic sites.