Sex predicts mortality after a breast cancer diagnosis, with male patients about one-fifth more likely than female counterparts to have died by the 5-year mark, finds a cohort study of more than 1.8 million patients. Clinical characteristics and undertreatment explained much, but not all, of this excess mortality.
“Studies have indicated that male patients with breast cancer had worse overall survival than their female counterparts, including those with early-stage disease, although results have been inconsistent,” the investigators note. However, “few studies have systematically investigated the factors associated with mortality in male patients with breast cancer or assessed whether breast cancer prognosis for men is congruent with that for women, accounting for the differences in clinical characteristics and treatment.”
Senior investigator Xiao-Ou Shu, MD, PhD, of the Vanderbilt Epidemiology Center, Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tenn., and coinvestigators conducted a nationwide, registry-based cohort study using the National Cancer Database to identify patients receiving a breast cancer diagnosis during 2004-2014. Analyses were based on 16,025 male patients (mean age, 63.3 years) having a median follow-up of 54.0 months and 1,800,708 female patients (mean age, 59.9 years) having a median follow-up of 60.5 months.
Results reported in JAMA Oncology showed that men had higher mortality across all stages (P less than .001 for each). Male patients also had poorer relative overall survival (45.8% vs. 60.4%, P less than .001), 3-year survival (86.4% vs. 91.7%, P less than .001), and 5-year survival (77.6% vs. 86.4%, P less than .001).
Age, clinical factors (tumor size; nodal status; stage, ER, PR, and HER2 statuses; histologic type; grade; lymphovascular invasion; OncotypeDX Breast Recurrence Score; and Charlson/Deyo score), and treatment factors (surgical procedure, chemotherapy, endocrine therapy, radiation therapy, and immunotherapy) collectively explained 63.3% of the excess mortality rate for male patients. They explained fully 66.0% of the excess mortality in the first 3 years after diagnosis, including 30.5% and 13.6% of that among patients with stage I and stage II disease, respectively.
However, even after adjustment for these factors plus race/ethnicity and access to care, men still had significantly higher risks of overall mortality (adjusted hazard ratio, 1.19), 3-year mortality (adjusted hazard ratio, 1.15), and 5-year mortality (adjusted hazard ratio, 1.19).
The database used did not contain information on causes of death or on cancer recurrence or progression events, precluding analyses of disease-free survival.
“Future research should focus on why and how clinical characteristics, as well as biological features, may have different implications for the survival of male and female patients with breast cancer,” Dr. Shu and coinvestigators recommended. “Additional factors, particularly compliance to treatment, biological attributes, and lifestyle factors (e.g., smoking, drinking, and obesity), should be assessed to help in developing treatments tailored for men, which would mitigate this sex-based disparity.”
Dr. Shu disclosed no relevant conflicts of interest. One author was funded by the program of the China Scholarship Council.
SOURCE: Wang F et al. JAMA Oncol. 2019 Sep 19. .