STEAP1 and Familial prostate cancer: One recently reported explanation for this phenomenon is that inhibited endocytosis can induce a selective increase in vesicular secretion of CD63.55 Another integral membrane protein called STEAP1 (six-transmembrane epithelial antigen of the prostate 1), a cell surface antigen for therapeutic targeting in prostate cancer, which has been reported in some PC3 cell lines and PC3 derived EVs,56,57 did not change with Sigma1 inhibitor treatment (Figure 7).