Cystatin A is a human cysteine proteinase inhibitor first identified from the cytosol of human polymorphonuclear granulocytes and has been shown to play roles in various cancers (i.e., colorectal cancer, breast cancer, non–small-cell lung cancer) and diseases (i.e., psoriasis, glaucoma) (30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42). The gene discussed is CSTA; the disease is breast cancer.