Gene-specific methylation profiles in male breast cancer

Background: Male breast cancer (MBC) is rare, but despite the rarity, morbidity and mortality in MBC patients is a serious concern. The role of the genetic factors in MBC pathogenesis is now well known. Mutations of BRCA1 and, mainly, BRCA2 have been found to significantly increase the risk of MBC. Conversely, the knowledge on molecular profiles of MBC is still incomplete. There is growing evidence that methylation plays an important role in breast cancer (BC) development and that characterization of tumor-specific methylation profiles may allow the identification of specific BC subtypes. Significant differences in tumor-associated gene methylation patterns have been related to receptor status (ER, PR and HER2) and different genome-wide DNA methylation profiles emerged between sporadic and BRCA1/2-associated BC. The contribution of DNA methylation in MBC pathogenesis have not yet well investigated. Using candidate-gene approach, we aimed to perform methylation analysis of a panel of BC-related genes, in order to identify biomarkers that could define MBC subgroups and elucidate pathways underlying MBC development. Materials and methods: Promoter methylation analysis of hTERT (human Telomerase reverse transcriptase), ESR1(Estrogen receptor 1), RASSF1(Ras association domain-containing protein 1), AR (Androgen receptor), MYC (v-myc avian myelocytomatosis viral oncogene homolog) and WNT1 (wingless-type MMTV integration site family, member 1) genes was performed in 69 male breast tumors and in 7 normal male breast tissues by Pyrosequencing, a highly sensitive and reproducible method, which provides absolute quantitative information on bases at each CpG site analyzed. Methylation levels were determined by calculating the average of methylation for each gene. Kruskal-Wallis test was used to identify significant differences in methylation levels among tumors stratified according to relevant clinical-pathologic features, including BRCA1/2 mutation. Results: Compared with normal tissues, hTERT, AR and RASSF1 showed higher methylation levels in tumors, whereas ESR1 showed lower methylation levels. No differences were observed in the methylation levels of MYC and WNT1. Higher methylation levels of RASSF1 were significantly associated with BRCA1/2 mutations (p = 0.008), HER2+ status (p = 0.01) and high tumor grade (G3) (p = 0.007). Higher methylation level of AR was significantly associated with BRCA1/2 wild-type status (p = 0.016) and lower methylation level of WNT1 was significantly associated with PR+ status (p = 0.014). Conclusions: Our results indicate that tumor-associated gene methylation patterns may identify specific MBC subgroups possibly related to BRCA1/2 mutation status. In particular, methylation of RASSF1, a tumor suppressor gene that mediates apoptosis, may identify a subgroup of MBC with an aggressive phenotype. Study supported by AIRC (IG 12780) to L.O. Citation Format: Piera Rizzolo, Valentina Silvestri, AnnaSara Navazio, Virginia Valentini, Veronica Zelli, Mario Falchetti, Ines Zanna, Simonetta Bianchi, Domenico Palli, Laura Ottini. Gene-specific methylation profiles in male breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4775. doi:10.1158/1538-7445.AM2015-4775