Strong cytotoxicity in breast cancer MDA‐MB‐231‐Luc and MCF‐7‐Luc cell lines by releasing cytokines, perforin, and granzyme B (in vitro). inhibition of tumour growth at a late stage in mice bearing MDA‐MB‐231 TNBC xenografts (in vivo). Here, GZMB is linked to breast cancer.