The rest of the SCLC cohort was composed predominantly of smokers with RB1−/TP53− SCLC (88%), smokers with the recently described RB1-proficient SCLC (RB1+/TP53−; 6%; ref. 4), and never-smokers with RB1−/TP53− SCLC (3%; described later). Here, RB1 is linked to small cell lung carcinoma.