Chronic inflammatory diseases and survival among breast cancer patients in the U.S. military health system

Purpose: There have been few studies on the relationship between chronic inflammatory diseases and breast cancer outcome. We evaluated the relationship between chronic inflammatory diseases and survival among breast cancer patients in the U.S. military health system (MHS), a universal healthcare system. Methods: The study used the Military Cancer Epidemiology database (MilCanEpi), which linked databases from the Department of War’s Central Cancer Registry (CCR) and the Military Health System (MHS) Data Repository (MDR). A total of 33 chronic inflammatory diseases were identified. A time-dependent Cox proportional hazard regression model was used to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs) of death associated with chronic inflammatory diseases while adjusting for potential confounders. Results: The final data included 14,258 patients with histologically confirmed primary breast cancer. Among them, 7883 had a diagnosis of chronic inflammatory diseases at or after breast cancer and 6375 had no diagnosis at any time in the data. A diagnosis of chronic inflammatory diseases was independently associated with a significantly increased risk of all-cause death after adjustment for confounders (adjusted HR = 1.76, 95% CI = 1.56–1.98). Notably, the increased risk of death associated with the inflammatory diseases persisted among stage-IV patients who usually died of breast cancer. The association was also observed regardless of age, comorbidity, hormone receptor status, timing of disease diagnosis relative to breast cancer diagnosis, or other characteristics. Conclusion: Chronic inflammation, characterized by chronic inflammatory diseases, was independently associated with increased all-cause death among breast cancer patients in MHS. Future research with cancer-specific death as the outcome is warranted.