149P - Risk of type II diabetes after breast cancer treatment: A 26-year population-based cohort study

Background

Contemporary data on the risk of developing type 2 diabetes (T2D) after breast cancer is needed to guide preventive management, especially according to the type of adjuvant cancer therapy. Among early-stage breast cancer patients, we evaluated the risk of T2D overall and according to cancer treatment.

Methods

Using Danish medical registries, we assembled a nationwide population-based cohort of early-stage breast cancer patients diagnosed 1996-2021 and aged ≥30 years. We created a comparison cohort of five breast cancer-free women for each woman with breast cancer, matched 6 months after the date of breast cancer diagnosis on age, region, and absence of pre-existing T2D. We followed both cohorts until a diagnosis of T2D, emigration, death, or December 31^st, 2022, whichever occurred first. We computed 5-year cumulative incidence proportions, the number needed to harm, and used Cox regression to calculate hazard ratios (HRs) of T2D, adjusting for comorbidity and marital status.

Results

Among 74,526 breast cancer survivors and 372,630 matched comparisons, the 5-year cumulative incidence proportions of T2D were 3.8% (95%CI=3.7-3.9) and 3.3 (95%CI=3.3-3.4), respectively, yielding an adjusted HR (aHR) of 1.07 (95%CI=1.04-1.10) and number needed to harm of 1 in 200. Adjuvant endocrine therapy (aHR=1.14; 95%CI=1.10-1.19), particularly aromatase inhibitor treatment (aHR=1.25; 95%CI=1.18-1.32) and to a lesser extent tamoxifen (aHR=1.05; 95%CI=0.99-1.11), was associated with elevated risk of T2D in women with breast cancer compared with matched breast cancer-free women. Breast cancer survivors who did not receive endocrine therapy did not have increased risk of T2D compared with matched breast cancer-free women. Within the breast cancer cohort, any chemotherapy (aHR=1.10, 95%CI=1.03-1.17) and radiation therapy (right-sided aHR=1.18, 95%CI=1.09-1.27 and left-sided aHR=1.24, 95%CI=1.15-1.33) were also associated with increased risk of T2D.

Conclusions

Breast cancer survivors had a modestly increased risk of T2D compared with women without breast cancer. The excess T2D risk seems to be largely driven by breast cancer therapy modalities.

Legal entity responsible for the study

Aarhus University.

Funding

The Novo Nordisk Foundation (Steno Collaborative Grant).

Disclosure

All authors have declared no conflicts of interest.