In addition, six genes were significantly enriched in MAPK signaling pathway (RPS6KA1, RAC2, CACNG4, CACNA1E, CACNA1H and MAPKAPK5, p = 1.93×10−5, FDR = 3.59×10−3), which was identified as a pivotal pathway for human cancer cell survival, dissemination and resistance to drug therapy [30], suggesting the potential role of this pathway on the intratumor heterogeneity formation of SCCB. The gene discussed is CACNA1E; the disease is urinary bladder small cell neuroendocrine carcinoma.