CD274 and cancer: Neither high PD-L1 expression, MMRd, or MSI are sufficient to drive immune checkpoint inhibitor (ICI) response, and benefit from ICIs has been observed in a non-trivial portion of biomarker-negative patients.1, 2, 3, 4 In particular, while up to 40% of MMRd/MSI cancers may demonstrate a response to ICIs, the prevalence of MMRd/MSI is infrequent across all cancer types, with most cancers having no or rare evidence of MSI.5