MKI67 and neoplasm: Other investigators have produced similar findings, demonstrating decreased tumour volumes and reduced proliferation in in vivo animal models of BC.100,101 Recently, Bojkova et al. showed that administration of metformin in a rat model with MNU-induced mammary tumours resulted in an increased proportion of low-grade tumours.102 A significant positive correlation between histological grade and Ki67 expression was noted.