The activation and tumor‐killing ability of NK cells rely on their secretion of pro‐inflammatory cytokines such as tumor necrosis factor‐alpha (TNF‐α) and interferon‐γ (IFN‐γ), and cytotoxins such as perforin and GZMB.[31, 32] To determine whether the antitumor activity of NK cells was also altered in CRC tumor tissues in addition to a reduction in cell number, we separated NK cells from tumor tissues or DNTs by magnetic bead sorting and quantified the mRNA expression levels of TNF‐α, perforin, GZMB and IFN‐γ in NK cells by qPCR after stimulating them with leukocyte activation cocktail. The gene discussed is GZMB; the disease is neoplasm.