MKI67 and breast cancer: In support of this, Δ40p53 expression was positively correlated with Ki67 expression (r = 0.4135, p < 0.0001) in 148 breast cancers (38 Grade 1, 38 Grade 2, and 72 Grade 3 IDCs [6]) (Fig. 6D), suggesting that high levels of Δ40p53 impact the proliferation of breast tumours.