Oct. 26, 2019
A Mayo Clinic study pinpoints unique practice patterns and prognosis factors in male breast cancer (MBC) and identifies health disparities associated with MBC. Investigators published the results online in the journal Cancer on Oct. 7, 2019.
"Furthering our understanding of male breast cancer treatment and prognosis is critical," says Kathryn J. Ruddy, M.D., medical oncologist at Mayo Clinic's campus in Rochester, Minnesota, who led the study with Siddhartha Yadav, M.B.B.S., a hematology and oncology trainee at the same campus. "There is an increasing appreciation that the tumor biology of male breast cancer differs from female breast cancer, and some studies suggest incidence of breast cancer in males may be rising."
Approximately 2,670 new invasive MBC cases will be diagnosed in the U.S. in 2019; lifetime breast cancer risk for men is about 1 in 833, according to the American Cancer Society. Knowing what influences men's prognoses and what health disparities exist currently may help develop more tailored treatment approaches, says Dr. Ruddy.
Dr. Ruddy points to a dearth of rigorous studies on this disease: no large, prospective, randomized clinical trials focused on MBC have been successfully completed to date.
Methods and findings
Dr. Ruddy and colleagues utilized the National Cancer Database to assess 10,873 U.S. men diagnosed with stages I-III breast cancer between 2004 and 2014, representing one of the largest MBC studies yet conducted. Median age at diagnosis was 64; median follow-up duration was 55 months. Approximately 90% had estrogen receptor positive (ER+) tumors, for which estrogen encourages growth. At diagnosis, 38% had stage I disease, 43% stage II and 19% stage III.
Study participants underwent the following treatments:
- 24% had breast conservation surgery; of those who had this surgery, 70% received radiation therapy
- 45% had chemotherapy
- 62% of patients with estrogen receptor positive disease received endocrine therapy
In 37% of patients with lymph node-negative, ER+/human epidermal growth factor receptor 2 (HER2)-negative tumors, physicians ordered tumor gene expression tests to assess disease recurrence and chemotherapy effectiveness.
Findings included treatment pattern changes over time, such as increasing rates of:
- Total mastectomy
- Contralateral prophylactic mastectomy
- Post-breast-conservation radiation
- Breast cancer recurrence and chemotherapy benefit prediction testing
- Anti-estrogen therapy
Though breast conservation surgery rates declined marginally over the study period, results indicated that this surgery is likely safe and effective for many men. For the research population, five-year overall survival rate was 79% and did not change significantly between 2004 and 2014. Median overall survival was 12 years across the whole group, with expected differences based on stage of disease: seven years for stage III MBC, 12 years for stage II and not yet determined for patients with stage I.
Further, the researchers discovered factors — black race, older age, multiple comorbidities, higher tumor stage and grade, and total mastectomy — associated with worse overall survival. Conversely, better overall survival was associated with:
- Progesterone receptor-expressing tumors
- Chemotherapy, radiation and anti-estrogen therapy
- Residence in a high-income area
The correlation between total mastectomy and poor overall survival may reflect the fact that men with larger tumors may have been more likely to have that surgery, according to Dr. Ruddy. There was a nonsignificant trend toward improved survival with use of adjuvant radiotherapy, but not for those who underwent total mastectomy, again likely due to the fact that patients with higher risk disease would have been more likely to choose that aggressive combination of treatments.
As MBC is a rare disease for which there is limited understanding of treatment patterns and prognostic factors, this study's significance lies in elucidating recent MBC treatments used, how MBC therapy is evolving and what impacts survival, says Dr. Ruddy. These may be useful to clinicians diagnosing and treating the disease.
"The racial, economic and age-related health disparities we found could inform future efforts to target interventions to optimize outcomes in men with breast cancer," she said.
Important questions remain with regard to optimal cancer therapies as well as how best to surveil breast tissue in men, both male breast cancer survivors and men at high risk of breast cancer based on a known deleterious genetic mutation. Dr. Ruddy is hopeful that the study she and Dr. Yadav led will help lay the groundwork for future clinical trials focused specifically on male breast cancer.
For more information
Yadav, S, et al. Male breast cancer in the United States: Treatment patterns and prognostic factors in the 21st century. Cancer. 2019. In press.
Key statistics for breast cancer in men. American Cancer Society.