PDCD6 and breast cancer: The four most abundant biotin-accessible surface proteins common to sEVs from MDA-MB-231 and MCF7 (GSTP1, EEF2, DOX10, and PGR) and two surface proteins common to mEVs from MDA-MB-231 and MCF7 (PDCD6, UTP20) may be explored for their potential as BC biomarkers in future studies.