RB1 and small cell lung carcinoma: In addition, different molecular subtypes of lung LCNEC have been described, with an SCLC-like subtype defined by the co-existence of retinoblastoma protein (Rb) loss and TP53 mutations without KRAS or STK11 mutations, and an adenocarcinoma-like subtype defined by the presence of KRAS or STK11 mutations [6,7,8,9,10].