Abstract PO1-16-10: BRCA mutated Male Breast Cancer, hallmarks of a distinct disease. Data from the Spanish Male Breast Cancer Registry (GEICAM/2016-04)
Authors: Martínez-Jáñez Noelia , Martínez Purificación , Hernando Cristina , Recalde Sabela , Sánchez Alfonso , Morales David , Santisteban Marta , Fernández Isaura , Barco Sonia Del , Zamora Esther , Iranzo Vega , Martos Tamara , Dueñas Eduardo Martínez-de , Novoa Silvia Antolin , Domínguez Severina , Domínguez Paula , Echarri Mª José , Bertrán Ana Santaballa , Mira Xavier , Blasco Andrea , Bezares Susana , Urriticoechea Ander 
Published: May 2024

Abstract
Background: Male breast cancer (MBC) accounts for approximately 0.25% of all male cancers and &lt; 1% of all BCs. Its incidence is increasing by 1.1% per year. Most population studies indicate that 10-15% of MBC patients (pts) have a germline BRCA2 mutation (BRCA2 mut). Around 5-10% of BRCA2mut male carriers will develop BC at their lives. Preliminary evidence suggests that BRCA2mut MBC pts tend to have a more aggressive disease. Here we present comparative series of MBC with and without BRCA to gain insight on differences between both groups. Methods: GEICAM/2016-04 (NCT03800355) is a retrospective, observational study which includes data from MBC pts diagnosed between 2000 and 2019 throughout Spain. This analysis includes the 1st unselected 186 pts included in the study, who had BRCA1/2 genes mutational status assessed within clinical practice. BC clinical subtypes are defined: luminal (HR+, HER2-), Triple Negative (TN) (HR-, HER2-), and HER2+ (HR+ or HR-); subtype is unknown in 6% pts. Results: 186 validated pts with BRCA1/2 testing were identified, representing the 24% of pts available in the database at the cut-off date (6-Mar-2023). 36 (19%) pts had germline BRCA1/2 mut (4 pts in BRCA1, 31 pts in BRCA 2 and 1 pt in both BRCA1 and BRCA2), and 150 (81%) pts had BRCA1/2 wild type (wt) or a variant of uncertain significance (VUS)/unknown (UK). Median age at BC diagnosis was 62 (34-87) years, 98% pts were Caucasian, and the median body mass index was 27 (18-46) Kg/m2 (overweight). Prior cancer history was reported in 6% BRCA1/2mut BC pts and 11% BRCA1/2wt or vus/uk, and family history included: 56% BC, 8% ovarian cancer, and 14% prostate cancer (PC). PC as part of prior medical history, cancer family history, and 2nd non-breast primary malignancy, was most frequent in BRCA1/2wt or vus/uk pts, with no statistical differences. At first diagnosis, stages III-IV were higher in BRCA1/2mut pts (28% vs. 17%, p=0.0093). Morphologically, invasive carcinoma of no special type (NST) was the most common pattern (92% in BRCA1/2mut vs. 86% in BRCA1/2wt or vus/uk), and lobular invasive carcinoma was not reported up-to-date. Histological grade 2 was the most frequent (54%), but grade 3 was present in 17/36 BRCA1/2mut pts. 88% pts received adjuvant treatment, 7% (neo-)adjuvant, 2% neoadjuvant and 3% did not receive any systemic therapy. Breast conserving surgery was performed in 4% (5/140) BRCA1/2wt or vus/uk EBC pts, and mastectomy was performed in 55% (n=6/11) de novo metastatic pts. In the advanced setting (n=38), visceral lesions were more frequent in BRCA1/2mut pts. Additionally, 92% BRCA1/2mut pts had ≤ 3 organs involved while one third of BRCA1/2wt or vus/uk pts had ≥ 4 metastatic locations. With a median follow-up of 64 months (mo.), median iDFS and DDFS were higher, but not statistically significant, in BRCA1/2wt or vus/uk pts vs. BRCA1/2mut pts. In advanced setting, median PFS to 1L-3L do not show statistically significant differences between both groups. Regarding OS, no differences were also observed, but the median values were not reached. Further detailed information according to BRCA1/2 mutational status and BC subtypes is included in the table below. Conclusions: In this subset analysis of GEICAM/2016-04, BRCA1/2mut pts had some features of worse prognosis, with a more prevalent de novo metastatic disease. No statistically significant differences were observed in outcomes in both early-stage and advanced setting vs. BRCA1/2wt or vus/uk pts. &lt;graphic&gt;

Citation Format: Noelia Martínez-Jáñez, Purificación Martínez, Cristina Hernando, Sabela Recalde, Alfonso Sánchez, David Morales, Marta Santisteban, Isaura Fernández, Sonia Del Barco, Esther Zamora, Vega Iranzo, Tamara Martos, Eduardo Martínez-de Dueñas, Silvia Antolin Novoa, Severina Domínguez, Paula Domínguez, Mª José Echarri, Ana Santaballa Bertrán, Xavier Mira, Andrea Blasco, Susana Bezares, Ander Urriticoechea. BRCA mutated Male Breast Cancer, hallmarks of a distinct disease. Data from the Spanish Male Breast Cancer Registry (GEICAM/2016-04) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-16-10.