To further confirm the function of CDK4/6 inhibitors in the chemoresistance and chemosensitivity of SCLC in vivo, we performed a tumorigenesis assay by injecting H69 and H69AR cells into the flanks of nude mice and treated the mice with chemotherapeutic drugs (cisplatin, 2.5 mg kg−1, i.p. injection; etoposide, 4 mg kg−1, i.p. injection) with or without PD (100 mg kg−1, administered by gavager on days 1–5, weekly). This evidence concerns the gene CDK4 and small cell lung carcinoma.