BREAST cancer is the most common type of cancer amongst females, and its risk could be influenced by metabolic abnormalities, hormonal precursors, and therapeutic interventions related to diabetes.
To assess whether a diagnosis of Type 1 or 2 diabetes increases the risk of breast cancer, Fanxiu Xiong, Department of Epidemiology and Biostatistics, University of California, San Francisco, USA, and colleagues performed a prospective population-based study. Between 2006–2010, they recruited 250,312 females aged 40–69 years from the UK Biobank group. Follow-up data was collected for Scotland, Wales, and England until 30 June 2018, 31 January 2019, and 30 June 2020, respectively. The first breast cancer diagnosis was the primary study outcome.
In total, there were 7,891 patients with prevalent Type 2 diabetes, 575 with prevalent Type 1 diabetes, and 6,821 patients with incident Type 2 diabetes. The remaining patients (n=235,025) did not develop diabetes during the study or have a diagnosis prior to study initiation. Adjusted hazard ratios (aHR) were calculated using multivariate Cox proportional hazards modelling to evaluate the relationship between breast cancer risk and diabetes. Age, race, BMI, smoking, Townsend deprivation index, and physical activity were the covariates adjusted for.
During the follow-up period there were 8,182 cases of breast cancer, of which 383 occurred in patients with diabetes. Overall, there was no increased breast cancer risk in patients with Type 2 diabetes (aHR: 1.0). However, the risk of developing breast cancer was highest during the first 5 years from Type 2 diabetes diagnosis (aHR: 3.9). Following this, a consistent decline in breast cancer risk was seen, and the relationship reversed after 10 years (aHR: 0.7).
For Type 1 diabetes, there was a greater risk of developing breast cancer in patients ≥60 years, as well as those who had had children, took hormone replacement therapy, had undergone mammography, and were post-menopausal (aHRs: 1.7, 3.0, 1.6, and 1.7, respectively).
Whilst the study identified that the breast cancer risk was elevated in the first 5-years following Type 2 diabetes diagnosis and suggested that patients with Type 1 diabetes may have a slightly increased breast cancer risk than those without diabetes (aHR: 1.5), overall, no significant relationship between diabetes and breast cancer risk was identified (aHR: 1.0).