The first attempts to identify SCLC subclasses based on their mutational profile [16,17,18] were not able to yield clear SCLC subtypes due to the abovementioned uniform genomic inactivation of TP53 and RB1, and to failure of other recurrent mutations (such as EP300, CREBBP, TP73, COL22A1, NOTCH1, MLL) to show reliable co-occurrence or mutual exclusivity. Here, RB1 is linked to small cell lung carcinoma.