RB1 and small cell lung carcinoma: Furthermore, LCNEC is a heterogeneous tumour, which can be divided into three genotypes: (i) an SCLC-like subtype with biallelic inactivation of TP53 and RB1, (ii) a non-small-cell-like subtype with mutations in TP53 and STK11/KEAP1, (iii) and a carcinoid-like subtype sharing the low TMB and MEN1 changes seen in lung carcinoids [2, 13, 17, 18, 21, 37, 48, 49].