Abstract PD7-13: Molecular characterization and mortality from breast cancer in men

Abstract

Abstract Background: Limited data exist on the molecular biology, treatment, and outcomes of breast cancer in men and much of our understanding in this area remains largely an extrapolation from data in women with breast cancer. Methods: We studied men and women with hormone receptor (HR)-positive breast cancer and 21-gene test (RS) results. Patients with negative nodes, micrometastasis, and 1-3 positive nodes were included. Differences in clinical characteristics and gene expression were determined and distribution of RS results was analyzed and correlated with 5-year breast cancer specific survival (BCSS) and overall survival (OS). Results: There were 3806 men and 571115 women. Men were older than women (mean age 64.2 vs. 59.1 years, p<0.001). RS <18 predominated in both genders, but RS ≥31 was more frequent in men (12.4% vs. 7.4%, p<0.001) as were very low scores (RS <11) (33.8% vs. 22.1%, p<0.001). Mean gene expression was higher in men for the ER, proliferation, and invasion groups. ER was lowest and PR highest in women <50 years, with a progressive increase in ER with age. Men <50 years had slightly lower ER and PR compared to older men. Survival data was available from SEER for 322 men and 55842 women. 5-year estimates for BCSS differed significantly between RS groups for both men (p=0.003) and women (p<0.001). For men, the 5-year BCSS was 99.0% and 95.9% with RS <18 and RS 18-30, respectively, and for women it was 99.5% and 98.6%, regardless of nodal status. RS ≥31 was associated with a 5-year BCSS of 81.0% in men and 94.9% in women. The prognostic utility of RS was evident in both men and women, despite the progressive increase in adjuvant chemotherapy use with higher RS results. 5-year BCSS and OS were overall lower in men than in women. Conclusion: This large genomic study reveals some distinctive biologic features of breast cancer in men and an important prognostic role for 21-gene testing in both men and women, regardless of nodal status. Future adjuvant trials in ER-positive breast cancer should focus on targeting endocrine-resistance in those patients with RS ≥31, and need to consider the weight of competing causes of mortality when investigating the value of any additional treatment beyond endocrine therapy. Citation Format: Massarweh SA, Sledge GW, Miller DP, McCullough D, Petkov VI, Shak S. Molecular characterization and mortality from breast cancer in men [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD7-13.