CTSL and breast cancer: Similarly, we identified a total of 274 proteins that showed luminal-specific secretion changes in one or both of the luminal cell lines (Fig. 2b; Additional file 11: Table S3), including decreased secretion of several members of the cathepsin family of globular proteases such as CTSB, CTSL, and CTSZ that were known to promote breast cancer progression and metastasis, [42] and the increased secretion of metastasis suppressor PEBP1 (a.k.a. RKIP) that showed luminal-specific intracellular expression.