Even after adjustment for undertreatment and differing clinical characteristics, men with breast cancer have higher mortality rates than women, report the authors of a nationwide cohort study.
The researchers, who are from Vanderbilt University Medical Center in Nashville, Tennessee, analyzed data obtained from the National Cancer Database on 1,816,733 patients diagnosed with breast cancer between January 2004 and December 2014. The patient population included 16,025 men and 1,800,708 women. The study's primary end point was overall survival, with secondary end points of three-year and five-year mortality. In analyzing the association between sex and mortality, the investigators factored in the roles played by race/ethnicity, clinical characteristics, treatments, and access to care, with adjustments made for age.
"Men diagnosed with breast cancer have 15% to 19% higher mortality than their female counterparts even after controlling for differences in clinical characteristics, socioeconomic status, and access to care," states Xiao-Ou Shu, MD, PhD, Associate Director for Global Health, Co-Leader of the Cancer Epidemiology Research Program, and Ingram Professor of Cancer Research at Vanderbilt University Medical Center. Dr. Shu is the senior author of the study, which has been published in JAMA Oncology.
Men with breast cancer had an overall survival rate of 45.8%, compared with 60.4% for women. Men also had lower rates of three-year survival (86.4% vs 91.7%) and five-year survival (77.6% vs 86.4%). Clinical characteristics and undertreatment accounted for a 63.3% excess mortality rate for men. These factors were associated with a higher proportion (66.0%) of excess deaths in men during the first three years following breast cancer diagnosis and in men with early-stage cancer (30.5% for stage I and 13.6% for stage II disease). However, even after adjusting for clinical characteristics, treatment factors, age, race/ethnicity, and access to care, sex was still a significant factor in overall mortality, with an adjusted hazard ratio of 1.19, and in both three-year and five-year mortality, with adjusted hazard ratios of 1.15 and 1.19, respectively.
Understanding the factors underlying the discrepancy "is fundamental to developing strategies for cancer treatment and survivorship care," write the researchers in their publication, led by first author Fei Wang, MD, PhD, of the Division of Epidemiology at Vanderbilt-Ingram Cancer Center. "These results suggest a need for further research into biological features of breast cancer and tailored treatments for men with the disease to mitigate the sex-based disparity in mortality."
"Differences in cancer biology, response and compliance to cancer retreatment, and post-cancer treatment lifestyle factors such as smoking, drinking, obesity, and physical activity may contribute to the sex disparity in mortality," remarks Dr. Shu. In their further investigation of the causes underlying the discrepancy, the researchers are currently evaluating the OncoType DX recurrence score differences between male and female breast cancer patients.
What advice does Dr. Shu have for oncologists as they seek to provide optimum treatment for men with breast cancer?
"Oncologists should encourage male breast cancer patients to completely follow their treatment plan and should closely monitor their compliance," she says. "They should also encourage patients to adopt and keep a healthy lifestyle, following the recommendations of the American Cancer Society."
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