Type 2 Diabetes and all-cause mortality among Spanish women with breast cancer

To explore the effect of type 2 diabetes mellitus (T2DM) on the risk of death among women with breast cancer (BC).

A survival analysis was conducted among a cohort of women diagnosed with BC between 2006 and 2012 in Spain (n = 4,493). Biopsy or surgery confirmed BC cases were identified through the state population-based cancer registry with information on patients' characteristics and vital status. Physician-diagnosed T2DM was confirmed based on primary health care clinical history. Cox regression analyses were used to estimate adjusted hazard ratios (aHR) and 95% confidence intervals (CI) for all-cause death. Analyses were adjusted for age, hospital size, several clinical characteristics (including BC stage and histology, among others) and treatment modalities.

Among the 4,493 BC women, 388 (8.6%) had coexisting T2DM. Overall, 1,299 (28.9%) BC women died during the completion of the follow-up and 785 (17.5%) did so during the first five years after BC diagnosis, resulting in a five-year survival rate of 82.5%. The death rate was higher in women with T2DM (43.8% died during whole period and 26.0% during the first five years) when compared with women without T2DM (27.5% and 16.7%, respectively). Accordingly, all-cause mortality was higher in women with T2DM (aHR: 1.22; 95% CI 1.03-1.44), especially if T2DM was diagnosed before BC (aHR:1.24; 95% CI 1.03-1.50) and in women with BC diagnosed before 50 years (aHR: 2.38; 95% CI 1.04-5.48).

T2DM was associated with higher all-cause mortality among Spanish women with BC, particularly when the T2DM diagnosis was prior to the BC.