Variant of prostatic adenocarcinoma with Paneth cell-like neuroendocrine differentiation readily misdiagnosed as Gleason pattern 5.

Summary This study focused on 11 cases of prostatic adenocarcinoma with Paneth cell–like change, which had sparse to no Paneth cell–like granules; grading the tumor conventionally would have resulted in assigning a Gleason pattern 5 for the primary or secondary pattern. Ten cases were entirely composed of the Paneth cell–like component. Architectural patterns included the following: nest and cord-like architecture (n = 4; 36.4%), nests only (n = 6; 54.5%), and cords only (n = 1; 9.1%). All 11 cases had amphophilic cytoplasm. Among the 11 cases, 7 had rare granules, 1 had 10% of the cells with granules, and 3 had no granules. Within the Paneth cell–like feature component, rare nucleolar prominence was seen in only 4 (36.4%) of 11 cases. Eight cases were diffusely positive for chromogranin and synaptophysin, 2 for chromogranin only, and 1 for synaptophysin only. In the 3 cases where performed, Ki-67 showed a very low rate of less than 5%. The keys to recognizing these cases are as follows: (1) nests and cords in a small focus, (2) deeply amphophilic cytoplasm with careful search in most cases revealing rare Paneth cell–like eosinophilic granules, (3) indistinct nucleoli, and (4) immunohistochemical staining for neuroendocrine markers. Based on follow-up from prior studies and the current work, these tumors appear to have a favorable prognosis. The importance of recognizing this variant of adenocarcinoma with Paneth cell–like differentiation is that if these tumors were graded conventionally, 9 of the 11 cases would have been assigned a misleading Gleason score of 5 + 5=10 or 5 + 4=9.