Post-menopausal women taking metformin for diabetes may be at lower risk of cancer

BUFFALO, N.Y. — Post-menopausal women who use metformin long-term for the treatment of diabetes may be at lower risk for developing certain cancers and dying from these diseases, reports a large prospective study from researchers at Roswell Park Cancer Institute (RPCI) and the University at Buffalo.

Their analysis was based on data from the Women’s Health Initiative (WHI), a series of large studies undertaken to address common health issues in women. The researchers also found that women with diabetes, compared to women without the disease, were more likely to develop cancer. The team’s findings were published in the International Journal of Cancer.

The research effort was led by Zhihong Gong, PhD, Assistant Professor of Oncology in the Department of Cancer Prevention and Control at Roswell Park, and Jean Wactawski-Wende, PhD, one of the principal investigators of the Women’s Health Initiative and dean of the School of Public Health and Health Professions at the University at Buffalo.

The investigators analyzed information from 145,826 post-menopausal women between 50 and 79 years of age from 40 U.S. clinical centers who participated in the WHI between 1993 and 1998.

They found that women with diabetes had a 45 percent greater risk of death from invasive cancer overall when compared to women without diabetes. In addition, among women with diabetes, the risk of cancer death differed significantly between metformin users and nonusers. The researchers noted a trend of decreasing risk of cancer death with increasing duration of metformin use.

Compared to women without diabetes, women with diabetes had a 13 percent higher risk of developing invasive cancer. These women also face increased risk that ranges from 20 percent to nearly double the chances of being diagnosed with the following cancers: colon, liver, pancreas, endometrial and non-Hodgkin lymphoma.

Results also show that metformin use was associated with better survival in diabetes patients diagnosed with ovarian, colorectal and breast cancer.

“In this large prospective study with long-term follow-up, we examined the association of diabetes and medications to treat the disease with the risk of cancer and cancer mortality overall and by cancer site,” says Gong.

“Our findings suggest that diabetes remains a risk factor for cancer overall and increases the risk of certain cancers. But we also found a lower cancer risk for certain cancers among those patients who have used metformin for many years,” Gong adds.

“The Women’s Health Initiative continues to offer thoughtful, meaningful data to researchers seeking to answer health care questions that impact our understanding of long-term health in older women,” says Wactawski-Wende.

The researchers say future studies are needed to further clarify the long-term impact of metformin on cancer risk and survival.

Research for the Women’s Health Initiative (WHI) has been supported, in part, by the National Heart, Lung and Blood Institute and the U.S. Department of Health and Human Services (HHSN268201100046C, HHSN268201100001C, HHSN268201100002C, HHSN268201100003C, HHSN268201100004C and HHSN271201100004C). Dr. Gong’s research is supported in part by the National Cancer Institute (K07CA178293).