RB1 and large cell neuroendocrine carcinoma: Genomic DNA was extracted from and PCR amplification was performed on genomic DNA or whole-genome amplification for KRAS, TP53, CDKN2A/p16, and RB1. In this study 5 of 10 LCNEC patients expressed PDX1 (pancreatic duodenal homeobox 1), 5 of 10 LCNEC also expressed PAX, a transcription factor expressed in well differentiated pancreatic neuroendocrine tumors.