HbA1c screening in patients with early breast cancer receiving endocrine therapy

Type 2 diabetes increases the risk of developing breast cancer, while endocrine therapy for early breast cancer may elevate the risk of type 2 diabetes. Studies suggest screening patients with early breast cancer receiving endocrine therapy for type 2 diabetes, but the optimal strategies remain unclear. We assessed haemoglobin A1c (HbA1c) screening adherence, the prevalence of HbA1c levels above the normal range (≥ 42 mmol/mol), and an HbA1c follow-up procedure.

Patients with early (stage I-III) breast cancer without diabetes receiving endocrine therapy were offered a single HbA1c screening test after treatment initiation at Aarhus University Hospital, Denmark, from October 2022 to April 2023. HbA1c ≥ 42 mmol/mol was classified as prediabetic (42-47 mmol/mol) or diabetic (≥ 48 mmol/mol). Patients and their general practitioners received standardised digital notifications if HbA1c ≥ 42 mmol/mol, recommending follow-up. Statistical analyses included Fisher's exact test and t-tests.

Of 174 patients offered HbA1c screening, 97 (56%) underwent testing. HbA1c ≥ 42 mmol/mol was detected in 11 patients (11% (95% confidence interval (CI): 5.8-19%)), including two patients with diabetic HbA1c levels (2.1% (95% CI: 0.3-7.3%)). Overweight (body mass index ≥ 25 kg/m²) and age ≥ 55 years correlated with HbA1c ≥ 42 mmol/mol. Most patients with HbA1c ≥ 42 mmol/mol (9 of 11) underwent primary-care follow-up.

Adherence to HbA1c screening may be affected if the test is an extra step for patients. Targeted HbA1c screening may be beneficial for patients with early breast cancer with overweight or older age receiving endocrine therapy. Further research is needed to improve implementation and participation.