BCAP31 and breast cancer: We first investigated the endogenous BCAP31 levels of different breast cancer cell lines and found a notable increase in BCAP31 expression levels in TNBC cell lines, such as MDA-MB-231 and MDA-MB-157 cells, which have higher invasive and metastatic capabilities than luminal cell lines, i.e., ZR-75-1, BT474, and MCF-7 cells, which have lower metastatic potential (Figure S2).