USP15 and neoplasm: The correlation coefficient between USP15 and SMAD7 (R = 0.11, p < 0.05) (Figure 4(c)) The Smad protein is the first detected kinase substrate of the TGF-β receptor, so we hypothesize that USP15 in BRCA most likely plays a role in promoting tumor development and metastasis via the TGF-β/smad signaling pathway.