Mortality rates after breast cancer diagnosis appeared higher among men than women across all stages of disease, according to results of a retrospective study published in JAMA Oncology.
Researchers attributed the disparity largely to undertreatment and clinical characteristics.
“The etiology of male breast cancer is largely unknown,” Xiao-Ou Shu, MD, PhD, Ingram professor of cancer research and professor of medicine at Vanderbilt University, told HemOnc Today. “Except for BRCA gene mutation, there is almost no known risk factor. Thus, it is difficult to identify high-risk men. More research that specifically focuses on male breast cancer is needed.”
In the large cohort study, Shu and colleagues used data from the National Cancer Database to compare mortality between 16,025 men (mean age, 63.3 years) and 1,800,708 women (mean age, 59.9 years) with breast cancer diagnosed between 2004 and 2014.
Researchers estimated the roles of ethnicity, clinical characteristics, treatments and access-to-care challenges with Cox proportional hazard regression models adjusted for age.
A higher proportion of men than women had late-stage breast cancer (stage III: 14% vs. 8.9%; stage IV: 5.8% vs. 3.8%), ER-positive disease (83.9% vs. 74.7%), ductal carcinoma (75.5% vs. 67.2%) and lymphovascular invasion (10.7% vs. 6.6%).
Endocrine therapy was used less frequently among men vs. women with ER-positive or PR-positive cancers (57.9% vs. 70.2%). Men also appeared less likely to receive radiotherapy, specifically among those who underwent breast-conserving surgery (64.9% vs. 78.6%) or had stage II or stage III disease and a mastectomy (38.6% vs. 43.7%).
OS served as the primary endpoint, with 3-year and 5-year mortality as secondary endpoints.
Median follow up was 54 months (range, 29.1-85) for men and 60.5 months (range, 34.3-92.6) for women.
Results showed an OS rate of 45.8% (95% CI, 49.5-54) among men vs. 60.4% (95% CI, 58.7-62) among women, with 3-year OS rates of 86.4% (95% CI, 85.9-87) vs. 91.7% (95% CI, 91.7-91.8), and 5-year OS rates of 77.6% (95% CI, 76.8-78.3) vs. 86.4% (95% CI, 86.4-86.5).
Clinical characteristics and undertreatment appeared associated with 63.3% of the excess mortality among men. Nevertheless, sex remained a significant factor in overall mortality (adjusted HR [aHR] = 1.19; 95% CI, 1.16-1.23), 3-year mortality (aHR = 1.15; 95% CI, 1.1-1.21) and 5-year mortality (aHR = 1.19; 95% CI, 1.14-1.23) after adjusting for clinical characteristics, treatment factors, access-to-care and ethnicity.
A lack of information on disease recurrence and causes of death served as the study’s primary limitations.
“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,” Shu and colleagues wrote. “Additional factors, particularly compliance to treatment, biological attributes, and lifestyle factors should be assessed to help in developing treatments tailored for men, which would mitigate this sex-based disparity.” – by John DeRosier
For more information:
Xiao- Ou Shu, MD, PhD, can be reached at Vanderbilt Epidemiology Center, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, 2525West End Ave., Suite 600,
Nashville, TN 37203-1738; email: email@example.com.
Disclosures: Shu reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.