In addition, tobacco and carcinogenic compounds can induce loss-of-function mutations in TP53,21 activate Myc and Bcl-2,81 and upregulate Sox2, CD133 and CD166 expression.82–84 Hence, the role of these carcinogens in promoting stemness and SCLC initiation remains to be further investigated. This evidence concerns the gene BCL2 and small cell lung carcinoma.