The utility of PSAP immunohistochemistry (IHC) for the determination of a tumor’s site of origin has been challenged by reports describing PSAP positivity in up to 40% of colorectal cancers [15], 33% of non-small cell lung cancer (NSCLC) samples [16], 30% of ovarian cancers [15], 10% of pancreatic cancers [15], 13% of breast cancers [16], 40% of renal cancers [16], and 68% of carcinoid tumors of the gastrointestinal tract [17]. The gene discussed is PSAP; the disease is breast carcinoma.