We identified obvious mosaic expression pattern of genes in these pathways, such as EGFR, TGFB2, IL6ST, BMPR2, PDGFA, FGFR1, FGF12, NOTCH2, JAG1, HSPA9, etc. These findings indicated that the expression level heterogeneity was existed across individual tumor cells of SCCB, inconsistent with the features of SCCB definition (purity component), which may compromise therapies targeting specific signaling. Here, FGFR1 is linked to urinary bladder small cell neuroendocrine carcinoma.