Metformin in the management of fibrocystic breast disease: a placebo-controlled randomized clinical trial

Fibrocystic disease (FCD) of the breast as a very common health problem in women has estrogen-dependent and proliferative features. No effective management strategy has been validated for this disorder, so far. The anti-hyperglycemic agent metformin has both anti-proliferative and estrogen-suppressing effects. Thus, we investigated metformin as a management strategy for FCD. The study was a double-blind placebo-controlled randomized clinical trial. Premenopausal women with FCD according to history, physical exam and ultrasound, who had measurable microcyst clusters on ultrasound (US) were entered the study. Oral placebo and metformin tablets (500 mg) were used twice daily by participants in the intervention and control groups. Size and number of microcyst clusters on US and the subjective pain score were recorded before and after the intervention. 154 participants were randomly allocated into two groups of 77 interventions and 77 controls. The decrease in size of the largest microcyst cluster in each patient and the mean decrease in number of microcyst clusters were not statistically significant (P = 0.310 and P = 0.637, respectively). However, those microcyst clusters which were ≥ 14 mm became significantly smaller after metformin use (P = 0.006). Additionally, in the subset of participants with pain at baseline, a larger proportion in the intervention group experienced at least 50% reduction in pain score (63.8% (30/47) in the intervention vs. 44.2% (19/43) in the placebo groups, P = 0.031). Our study showed that metformin might be effective in the management of FCD. Further studies are proposed for confirmation of this subject.