A new study has reported that tamoxifen use appears to increase the risk of developing type 2 diabetes in older breast cancer survivors. This is the first study to show an association between tamoxifen and diabetes. While increasing evidence links breast cancer and diabetes, few studies have explored possible links between cancer treatments and risk of diabetes. It is plausible that tamoxifen could increase diabetes incidence through its estrogen-inhibiting effects since estrogen plays a role in blood sugar control.

To conduct the study, the authors used data from health databases in Ontario, Canada to identify 14,360 women over 65 who were diagnosed with early-stage breast cancer between April 1, 1996 and March 31, 2006. The average age was 74.9 years. Survivors who were diagnosed with diabetes during follow-up were age-matched with up to five survivors who did not develop diabetes. The authors then compared the likelihood of diabetes between tamoxifen users and tamoxifen nonusers (after adjusting for other diabetes risk factors). The authors also compared diabetes risk in aromatase inhibitor users compared to nonusers.

A total of 1,445 (10%) of the study population developed diabetes during follow-up lasting an average of 5.2 years. Current tamoxifen use was found to be associated with 1.24 times higher risk of diabetes compared with no tamoxifen use. On the other hand, no association was found between aromatase inhibitor use and diabetes. The authors conclude that current tamoxifen therapy is associated with an increased incidence of diabetes in older breast cancer survivors. The findings suggest that tamoxifen may exacerbate an underlying risk of diabetes in susceptible women. Further studies are needed to better explore this association.

Please see our articles on what to eat during tamoxifen treatment and how breast cancer is related to diabetes for more information on how to optimize treatment with aromatase inhibitors and reduce side effects.