CDK4 and small cell lung carcinoma: Here, Rb1flox/flox, Trp53flox/flox, Ptenflox/flox (RTP) and Rb1flox/flox, Trp53flox/flox, MycLSL/LSL (RPM) spontaneous SCLC mouse models, SCLC cell line‐derived xenograft (CDX) models, and SCLC patient‐derived xenograft (PDX) models are established to reveal the potential effects of CDK4/6is on SCLC chemoresistance.