Crumley S, et al. - As high levels of microsatellite instability, tumor expression of PD-L1, high tumor mutation burden, and increased tumor-infiltrating lymphocytes have been associated with response to checkpoint inhibitor blockade, researchers investigated if a subset of microsatellite-stable endometrioid endometrial carcinomas has higher immune cell infiltrates and/or expression of PD-L1. Outcomes support the existence of a subset of microsatellite-stable endometrial cancers having higher expression of PD-L1 and increased tumor-associated CD3+ and CD8+ lymphocytes, these characteristics are more commonly associated with endometrial cancers with high levels of microsatellite instability. Results thereby suggest that patients who could potentially benefit from this therapeutic approach might be excluded via screening strategies to select only microsatellite instability-high advanced endometrial cancers for checkpoint inhibitor therapy.