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Metformin combination slightly lowers breast cancer risk among women with diabetes
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A lower risk for breast cancer was found among women who used metformin in combination with other diabetes drugs compared with those using metformin alone, according to recent study findings published in BMJ Open Diabetes Research & Care.
However, the risk for overall cancer did not differ between women on metformin and those on other diabetes drugs, according to the researchers.
Reina Haque, PhD, of the Southern California Permanente Medical Group, and colleagues evaluated data on 66,778 women (mean age, 56 years) with type 2 diabetes (median duration, 6 years) who were members of Kaiser Permanente Southern California to determine the effect of metformin on the risk for breast, endometrial and ovarian cancer.
Reina Haque
Participants were divided into categories based on drug use: metformin-only users (n = 4,887), metformin combination users (n = 22,037), non-metformin users (n = 14,865) and non-diabetes medication users (n = 24,989).
Overall, 1,572 participants developed breast cancer, 348 developed endometrial cancer, 163 developed ovarian cancer, 7,826 died, 22,943 disenrolled from the health plan and 33,926 reached the end of the study. Median follow-up for all participants was 6 years.
The highest rate for breast cancer was found among non-metformin combination users (5.37 per 1,000 person-years), followed by metformin-only users (5.01 per 1,000) and non-metformin users (3.95 per 1,000). Non-metformin combination users (1.29 per 1,000) and metformin-only users (1.26 per 1,000) had the highest rates of endometrial cancer.
Compared with metformin-only users, metformin combination users had a lower overall risk for breast cancer (adjusted HR = 0.85; 95% CI, 0.69-1.04). Among participants with better controlled HbA1c, the risk for breast cancer was lower; however, there was no protective effect among participants with higher HbA1c (adjusted HR = 1.06; 95% CI, 0.73-1.55).
“In summary, we observed a slightly lower breast cancer risk among women with type 2 diabetes who used a combination of antidiabetic medications with metformin compared with metformin only users; however, the results were not statistically significant,” the researchers wrote. “Overall, our results do not strongly support metformin monotherapy for cancer chemoprevention. Larger studies with a longer follow-up are needed to evaluate metformin’s potential effect on other gynecological cancers.” – by Amber Cox
Disclosure: The researchers report no relevant financial disclosures.
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