CircRNA cESRP1 was sensitized to small cell lung cancer (SCLC) cells upon chemotherapy (i.e., doxorubicin, CDDP and etoposide) by sponging miR-93-5p, and upregulating expression of the miR-93-5p downstream target, Smad7/p21(CDKN1A). Here, CDKN1A is linked to small cell lung carcinoma.