PRF1 and triple-negative breast carcinoma: Serine protease granzymes are expressed mainly in NK cells and toxic T lymphocytes and kill tumor cells along with perforin once they are secreted from immune cells.48 Wang et al. reported that granzyme B derived from T cells activates caspase-6 in triple-negative breast cancer cells, which further cleaves GSDMC at the Asp365 residue.46 However, the importance of tumor-derived granzyme B is largely unknown because of its relatively low expression in tumor cells.