Objectives Recent evidence suggests that hyperinsulinemia associated with obesity may be a significant risk factor for the development of endometrial cancer. Metformin is used in type II diabetes to lower circulating insulin levels. We sought to examine our obese patients with endometrial cancer and examine those who were on metformin to determine any impact on their cancer course.

Methods A retrospective review of all women with the diagnosis of endometrial cancer and a body mass index of 30 kg/m² or higher during a 6-year period (2005–2011) at our institution was conducted. Records were reviewed for standard demographic data, use of metformin, cancer characteristics, treatment, and cancer follow-up.

Results A total of 351 women were identified who were obese and diagnosed as having endometrial cancer. Of these, 64 were on metformin (M+) at the time of diagnosis of endometrial cancer. The women on metformin had a significantly higher mean body mass index (44.6 vs 41.6, P < 0.05). Age, grade, stage, and adjuvant therapy did not differ between the 2 groups. Recurrence occurred in 15.3% of the M- women versus 7.8% of the M+ women (not significant). However, for those patients with type I endometrial cancer, only 1 patient (1.9%) who was on metformin recurred versus 10.3% who were not on the drug (P = 0.05). With a minimum of 24 months of follow-up, 89.1% of metformin users were alive and free of disease versus 83.9% of nonusers (not significant).

Conclusions Obese women who developed endometrial cancer while on metformin did not seem to have pathologic risk factors different from those not on metformin. However, the type I cancer patients on metformin were less likely to recur than those not on the drug. This suggests that a prospective trial of metformin at the time of diagnosis of endometrial cancer in the obese population may be warranted.