The response was measured by change in Ki-67, a cellular proliferation marker, and individual women varied in their response.8 In exploratory subgroup analyses, associations with body mass index were observed; leaner women showed a greater Ki-67 change post-treatment than obese women.8,9 Heterogeneity of response to metformin has been documented in other pre-surgical window studies in endometrial,9–12 breast13–15 and prostate cancer16 and is likely to be related to both patient- and tumour-associated factors. Here, MKI67 is linked to neoplasm.