The pRb pathway in aSCLC was further investigated via gene pathway analysis by RNA-seq, which revealed major upregulation of the proproliferative G2M checkpoint and E2F target signatures in aSCLC, at a level markedly exceeding that found in a control set of carcinoid tumors and in some cases reaching the level seen in conventional sSCLC (Supplementary Fig. S12C). Here, RB1 is linked to carcinoid tumor.