Causes of death after breast cancer diagnosis: A US population-based analysis

Background: The focus on noncancer causes of death in patients with breast cancer (BC) remains superficial. The objective of the current study was to assess and quantify causes of death after BC diagnosis. Methods: In total, 754,270 women with BC in the United States who were diagnosed during 2000 through 2015 and retrieved from the Surveillance, Epidemiology, and End Results (SEER) program were studied. Standardized mortality ratios (SMRs) for causes of death were calculated. Results: Of the included patients, 183,002 (24.3%) died during the follow-up period. The greatest proportion of deaths (46.2%) occurred within 1 to 5 years after diagnosis. Most deaths occurred from BC itself or from other cancers, and the number of BC deaths decreased as more years passed after diagnosis. The most common noncancer causes of death within <10 years after diagnosis were heart diseases followed by cerebrovascular diseases. However, >10 years after diagnosis, the most common noncancer causes of death were heart diseases followed by Alzheimer disease. Patients had a statistically significant higher risk of death from chronic liver diseases within 5 to 10 years after diagnosis compared with the general population (SMR, 1.23; 95% CI, 1.09-1.38) and had statistically significant higher risks of death from Alzheimer disease (SMR, 1.21; 95% CI, 1.14-1.29) and from diseases of the heart (SMR, 1.06; 95% CI, 1.02-1.09) >10 years after diagnosis. Conclusions: Although BC remains the most common cause of death after BC diagnosis, other non-BC causes of death (mainly heart and cerebrovascular diseases) represent a significant number of deaths among patients with BC. These findings provide important insight into how BC survivors should be counselled regarding future health risks.