Multivariate analyses identified BC patients with intratumoral LAG3+ TIL as having significantly improved BC specific survival (BCSS) (hazard ratio (HR): 0.71, 95% confidence interval (CI) 0.56–0.90), particularly if they were ER-negative (HR: 0.50, 95% CI 0.36–0.69). Here, LAG3 is linked to breast cancer.