DPP4 and neoplasm: In evaluating SCLC, we combined the GTEx database (including 288 normal lung samples) and the cBioPortal dataset (81 SCLC RNA-seq data) to make comparisons and the results indicated that 7 genes (TMEM187, WSCD1, MRPL44, PARP11, PARP1, DEPDC1B and CKAP2) were enriched, while 6 genes (POLD4, CAB39, PDPK1, DPP4, TIPRAP, and STRA13) were down-regulated in tumor samples (Supplementary Figure S5B).