Small cell carcinoma of the prostate is associated with poor prognosis and different treatment from conventional acinar adenocarcinoma. Given the important clinicopathologic implications of a diagnosis of small cell carcinoma, we report 7 cases showing unusual, extensive small cell like change in intraductal carcinoma and invasive carcinoma. Prostatic biopsies from 3 patients and radical prostatectomy specimens from 4 patients showed variably extensive small cell like high-grade prostatic intraepithelial neoplasia and intraductal carcinoma. Five cases were associated with conventional acinar adenocarcinoma (2 cases with Gleason score 4 + 3 = 7; 3 cases with Gleason 3 + 4 = 7). No small cell carcinoma was seen. Small and large ducts with small cell like change showed solid and cribriform proliferations of atypical cells with abrupt transition between centrally located populations of small cells and more typical large dysplastic cells at the duct periphery. Rosette-like formations were noted within some involved ducts. Small cell like change was characterized by crowded cells with uniformly bland vesicular nuclei and minimal cytoplasm and no significant mitotic or apoptotic activity. In 3 cases, similar small cell like morphology was noted focally in invasive carcinoma. The small cell like areas were negative for synaptophysin and chromogranin, focally positive for TTF-1, and weakly positive for racemase. Ki-67 labeled less than 5% with predominant labeling of the larger atypical cells and minimal reactivity in the small cell like population. In summary, small cell like change in prostatic intraepithelial neoplasia, intraductal carcinoma, and invasive carcinoma is not associated with small cell carcinoma; shows no immunohistochemical evidence of neuroendocrine differentiation; and likely is not an adverse prognostic feature. (C) 2013 Elsevier Inc. All rights reserved.