NK cell infiltration is associated with improved overall survival in solid cancers: A systematic review and meta-analysis

•NK cell infiltration to solid tumors independently predicts improved OS.•We reviewed 53 studies and meta-analyzed hazard ratios from 30.•Meta-analysis revealed that NK cell infiltration predicts decreased risk of death.•NK prognostic value is related to identifying marker and subtumor location.•NK cell infiltration may be associated with tumor stage and grade. The immune landscape of a tumor is highly connected to patient prognosis and response to treatment, but little is known about how natural killer (NK) cells predict overall survival (OS) among patients with solid tumors. We present the first meta-analysis on NK cell infiltration into solid tumors as a prognostic indicator for OS, considering cancer types independently, and together. Samples were collected from 1973 to 2016 with results published between 1989 and 2020. From 53 studies, we found that NK cell infiltration corresponds with decreased risk of death (HR=0.34, 95% CI: 0.26–0.46; p