Demographic Characteristics, Survival and Prognostic Factors of Early Breast Cancer Patients with Type 2 Diabetes Mellitus: A Hospital-Based Cohort Study

OBJECTIVE: With increasing prevalence of type 2 diabetes mellitus and breast cancer in Iran, we aimed to search hospital registries of breast cancer patients to investigate type 2 diabetes mellitus association with survival outcomes of early breast cancer after adjustment of confounding factors. METHODS: In a retrospective cohort study conducted from July 2003 to Feb 2014 and followed up until death or December 2016, female patients with early breast cancer who have been treated for the first time at the Cancer Institute of Iran, were divided to diabetic and non-diabetic groups. Primary and secondary outcomes were relapse free survival (RFS) and overall survival (OS). SPSS version 23 was used for analysis of data. Other variables included age, tumor stage, hormone receptor status, tumor subtype, and patient’s body mass index (BMI). RESULT: From a total of 1021 patients, 218 (21.4%) had type 2 diabetes mellitus. Diabetic patients had a higher mean age (53.31 vs 47.00), higher mean BMI (31.13 vs 29.15), lower HER2 expression (20.8% vs 32.1%) and higher frequency of luminal A subtype (61.1% vs 51.0). Overall, after adjustment of other variables, diabetes status did not affect RFS or OS independently. However, in luminal A subgroup, patients with diabetes mellitus had significantly lower survival outcomes of OS (135.277 vs 154.701) and RFS (114.107 vs 133.612) as well as OS higher hazard ratio of 1.830 and RFS hazard ratio of 1.663 compared to non-diabetic patients. BMI, hormone receptor status and tumor stage significantly affected the survival of the patients. CONCLUSION: In the present study, in addition to known breast cancer risk factors, BMI and type 2 diabetes mellitus had an independent impact on survival of the patients, highlighting the importance of health issues such as obesity and diabetes suboptimal performance in the treatment outcomes of early breast cancer patients in Iran.