MKI67 and neoplasm: PCNA regulates DNA replication via interactions with DNA polymerase delta, and is a marker of cellular proliferation often assessed during routine histopathology analyses of tumor tissues along with MKI67 to determine the proliferative indices of tumor cells in situ.25 Indeed, we previously observed4 that pretreatment tumor tissues from metformin responders exhibited elevated MKI67 expression levels vs nonresponders (47.3% vs 24.9%, P‐value = .004), providing suggestive evidence that these patients may harbor tumor cells with a greater proliferative capacity.