PSAP and prostate cancer: PSAP staining was almost exclusively seen in prostate cancers, with PSAP positivity in 96.9% of 15,455 prostate cancers, and only occurred in 2 of the 127 evaluated extra-prostatic tumor categories (diffuse-type gastric adenocarcinoma and neuroendocrine tumors of the pancreas; Table 1, Supplementary Figure S1).