PENK and small cell carcinoma: The identified prostate stromal-specific factor proenkephalin (PENK) was cloned, and transfected into scTF+B2Mlo stem-like small cell carcinoma LuCaP 145.1, reprogrammed luminal-like scTF−B2Mhi LNCaP, and luminal-like scTF−B2Mhi adenocarcinoma LuCaP 70CR.