Small cell carcinoma of the prostate: an immunohistochemical study.

Small cell carcinoma of the prostate (SCPC) is morphologically similar to small cell carcinoma of the lung (SCLC) and maybe misinterpreted as Gleason pattern 5b prostate adenocarcinoma (HGPC). Recognition of SCPC is important because of its different clinical behavior. This study aims to characterize the immunophenotype of histologically classic SCPC using a comprehensive panel of markers, to better understand its histogenesis, aid in its classification, and evaluate potential therapeutic targets. Using the World Health Organization morphologic criteria for SCLC, 18 SCPC cases were identified; and studied for the following tumor marker groups: prostate specific/related, neuroendocrine, sex steroid hormone receptors, and prognostic/treatment target-related. Ten cases of UPC were used as controls. PSA was positive in 17% of SCPC and neuroendocrine markers were expressed in HGPC. PSA, TTF-1 and CD56 were the most helpful markers in differentiating between SCPC and HGPC (P<0.01), whereas bombesin/GRP, c-kit, bcl-2, and EGFR expression was more frequent in SCPC. SCPC is best diagnosed by following the World Health Organization diagnostic criteria for SCLC. Immunohistochemical markers can help separate SCPC from HGPC and may be useful in histologically borderline cases. Potential therapeutic targets are identified immunohistochemically in SCPC (Bombesin/GRP, c-kit, bcl-2, and EGFR).