Metformin prevents endometriosis in breast cancer patients

Australia: Metformin appears to prevent endometrial changes induced by tamoxifen, and has favorable metabolic effects in breast cancer patients, according to a new study published in the journal Clinical Endocrinology.

Susan R. Davis, School of Public Health and Preventive Medicine, Monash University, Melbourne, Victoria, Australia, and colleagues conducted this randomized placebo-controlled trial to determine whether metformin prevents tamoxifen‐induced endometrial changes and insulin resistance (IR) after a breast cancer diagnosis.

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Tamoxifen is an endocrine therapy used for the treatment of breast cancer. Although an estrogen antagonist in the breast, tamoxifen is an estrogen agonist in the endometrium. The mean endometrial thickness (ET) has been reportedly known to increase in the first year of tamoxifen, it is also associated with endometrial hyperplasia (EH), endometrial polyps, and endometrial cancer. Compared with nonuse of the drug after breast cancer, its use causes 2– to 7–fold increase in the risk of endometrial cancer after 2 and 5 years of tamoxifen treatment.

For the study, 102 postmenopausal women with hormone receptor-positive breast cancer taking tamoxifen were randomized to receive metformin 850 mg or identical placebo, twice daily, for 52 weeks. The 101 women who took at least one dose of medication were aged 56 (43–72) years, with 5(0.5–28) years postmenopause, and had taken tamoxifen for 28.9 (0–367.4) weeks.

Outcome measures included a double endometrial thickness (ET) measured by transvaginal ultrasound, fasting insulin, glucose and IR estimated by the homeostasis model of assessment (HOMA-IR).

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Key Findings:

• The baseline ET was 2.9 mm (1.4–21.9) for the placebo group (n = 52) and 2.5 mm (1.3–14.8) for the metformin group (n = 50).


• At 52 weeks, the median ET was statistically significantly lower for the metformin (n = 36) than for the placebo group (n = 45) (2.3 mm (1.4–7.8) vs 3.0 (1.2–11.3); P = 0.05).


• 13.3% allocated to placebo had an ET greater than 4 mm vs 5.7% for metformin.


• There was no endometrial atypia or cancer.


• Compared with placebo, metformin resulted in significantly greater baseline-adjusted reductions in weight, waist circumference (0.03) and HOMA-IR.

"Further research into the adjuvant use of metformin after breast cancer and to prevent EH and cancer is warranted," concluded the authors.

For further reference follow the link: https://doi.org/10.1111/cen.13830