Association between tamoxifen treatment and diabetes

Abstract

BACKGROUND: There is increasing evidence linking breast cancer and diabetes; however, few studies have explored the association between cancer treatments and risk of diabetes. Tamoxifen may increase diabetes incidence through its estrogen-inhibiting effects. This study assessed whether tamoxifen treatment in older breast cancer survivors is associated with an increased risk of diabetes. METHODS: This nested case-control study used population-based health databases in Ontario, Canada to identify women older than 65 years with early stage breast cancer between April 1, 1996 and March 31, 2006. Cases were defined as cohort members diagnosed with diabetes during follow-up (March 31, 2008), and each case was age-matched with up to 5 controls who did not develop diabetes. After adjusting for other risk factors, the authors compared the likelihood of diabetes between current tamoxifen users and tamoxifen nonusers, based on prescriptions at diabetes diagnosis. They also compared diabetes risk in current aromatase inhibitor users versus nonusers. RESULTS: Of 14,360 breast cancer survivors identified, mean age 74.9 years, 1445 (10%) developed diabetes over a mean follow-up of 5.2 years. Current tamoxifen therapy was associated with a significantly higher risk of diabetes compared with no tamoxifen therapy (adjusted odds ratio, 1.24; 95% confidence interval, 1.08-1.42; P =.002). There was no association between aromatase inhibitor therapy and diabetes. CONCLUSIONS: Current tamoxifen therapy is associated with an increased incidence of diabetes in older breast cancer survivors. These findings suggest that tamoxifen treatment may exacerbate an underlying risk of diabetes in susceptible women; further studies are needed to better explore this association. Cancer 2011. © 2011 American Cancer Society. There is evidence that estrogen deficiency may increase the risk of diabetes, which has implications for breast cancer patients being treated with adjuvant hormonal therapy. This population-based nested case-control study from Ontario, Canada, of 14,360 breast cancer survivors aged 66 years or older finds that current tamoxifen treatment is associated with a significant increase in the incidence of diabetes compared with no tamoxifen treatment (adjusted odds ratio, 1.24; 95% confidence interval, 1.08-1.42; P =.002). Copyright © 2011 American Cancer Society.