METFORMIN OFFERS NO SURVIVAL BENEFIT IN OLDER BREAST CANCER PATIENTS 

NEW YORK (Reuters Health) May 10 - In older breast cancer patients with recent-onset diabetes, cumulative metformin duration is not associated with survival, according to Canadian researchers.

In an April 30 online paper in Diabetes Care, Dr. Illiana C. Lega of Women's College Hospital, Toronto, and colleagues noted that metformin has been associated with a reduction in breast cancer risk. Also, they said, there's been speculation that metformin might improve survival after cancer through direct and indirect tumor-suppressing mechanisms - although findings have been inconsistent (see Reuters Health report of June 14, 2012).

Because pre-existing diabetes may increase the risk of death by as much as 40% in cancer patients, and as many as 16% of breast cancer patients may have pre-existing diabetes, any relationship is of particular importance, the authors wrote.

They used Ontario health care data to identify 2,361 women age 66 or older with diabetes and breast cancer. The mean age at cancer diagnosis was 77.4 years.

Over an average follow-up of 4.5 years, 1,101 patients died (46.6%), including 386 (16.3%) whose deaths were cancer-related.

There was no significant association between cumulative duration of past metformin use and all-cause mortality (adjusted hazard ratio 0.97). There was a possible indication of some reduction in breast cancer specific mortality (hazard ratio 0.91) but this too was not statistically significant.

Thus, as Dr. Lega summarized in an email to Reuters Health, "We were unable to show a significant association between improved survival and increased cumulative metformin duration in a select population of older breast cancer patients with diabetes."

"More understanding of metformin's effect on breast cancer is essential to help address the disparity in cancer outcomes between patients with and without diabetes and to help guide diabetes treatment," Dr. Lega said.

SOURCE: http://bit.ly/10gCEa3

Diabetes Care 2013.