Abstract Introduction: Male BC is a rare disease (dx) for which management is extrapolated from trials in female BC. Comprehensive prospective data about QoL in men with BC could inform treatment. The international Male BC Consortium conducted a prospective registry of male BC patients of all stages who newly presented to a participating center between October 2013 and February 2017. A QoL substudy was conducted as part of this registry at most participating sites. Methods: Informed consent for participation in the QoL substudy was requested from new enrollees. Those who consented were asked to complete a survey including the EORTC QLQ-C30 and BR23 (breast cancer specific module), adapted by replacing female-specific items with male-specific sexual activity/function items from the prostate module (PR25). Outcomes were scored according to standard EORTC QLQ procedures on a 0-100 scale (with higher scores on QoL/functioning scales representing better QoL and functioning, and higher scores on symptom scales representing worse symptoms). Forms were analyzed centrally by EORTC. In order to compare to female BC, we used reference data from 2782 mixed age (62% under age 60) women with BC (of whom 1,147 had recurrent or metastatic dx, and 464 had stage 1-2 dx) reported in the EORTC QLQ-C30 Reference Values manual (2008). Results: A total of 557 men were enrolled in EORTC10085, 445 at sites participating in the QoL substudy. Consent forms were received from 422/445 (95%) for the substudy. Baseline survey (required to be completed within 30 days of enrollment) compliance was 85% (359/422). Median age at diagnosis was 67 years. There were 111 men (45%) with node-positive M0/MX dx and 27 men (8%) with M1 dx. Their median global health status score at baseline was 75 (IQR 67-83), higher than that documented historically in female BC (67, with IQR 50-83, in both the 2782 women with mixed stage and the subgroup of 464 with stage 1-2 tumors). The participating men's median social functioning score was 100 (IQR 67-100), also higher than the 83.3 (IQR 67-100) reported in mixed stage female BC patients, though no different than the 100 (IQR 67-100) found in women with stage 1-2 dx. Men's most commonly reported symptoms included fatigue (median score 13.9, IQR 0-33), insomnia (median score 0, IQR 0-33), and pain (median score 0, IQR 0-33), for which women's median scores were 33 (IQR 11-44), 33 (IQR 0-33), and 17 (IQR 0-50) with mixed stage dx, and 22 (IQR 0-33), 33 (IQR 0-33), and 17 (IQR 0-33) with stage 1-2 dx. Men's median sexual activity score was 33.3 (IQR 0-50), with less sexual activity reported by older patients and men with M1 dx. In those who were sexually active, median sexual function score was 83 (IQR 75-92), with no difference by age or stage. Conclusions: QoL and symptom burden in male BC patients appears no worse (and possibly better) than that in female patients. Future analyses of 1- and 5-year surveys from this study will assess the impact of specific treatments on changes in symptoms and QoL over time. These data will be useful in future efforts to tailor treatments and target interventions for male BC. Funding: Breast Cancer Research Foundation, Dutch Pink Ribbon Foundation, Swedish BRO, and EBCC Council. Citation Format: Schroder C, Cardoso F, Dijkstra N, van Leeuwen-Stok E, Linderholm B, Morgenstern D, Van Poznak C, Wolff AC, Poncet C, Gomez HL, Aalders K, Bjelic-Radisic V, Werutsky G, Tryfonidis K, Coens C, Giordano SH, Ruddy KJ. Quality of life (QoL) in male breast cancer (BC): Prospective study of the EORTC10085/TBCRC029/BIG2-07/NABCG International male BC program [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 P5-23-02.