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

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.