Tumor suppressor genes TP53 and RB1 were universally inactivated in SCLC, which was once considered a molecularly homogeneous tumor [7], In recent years, the importance of MYC family, KMT2D, PIK3CA, and other gene mutations has been confirmed in patients, xenograft tumor models, mice, and cell levels. The gene discussed is PIK3CA; the disease is small cell lung carcinoma.