DNA methyltransferase 1, 3a, and 3b affect DNA methylation, and it is thought that they play an important role in the malignant transformation of various
cancers. The current study was designed to analyze
DNA methyltransferase expression by immunohistochemistry in a series of 94 Tunisian sporadic
breast carcinomas. Results were correlated to clinicopathologic parameters and promoter methylation status of 8 tumor suppressor genes (BRCA1, BRCA2, RASSFA1, TIMP3, CDH1, P16, RARĪ²2, and DAPK). Overexpression of
DNA methyltransferase 1, 3a, and 3b was detected in 46.8%, 32%, and 44.7% of cases, respectively. A significant correlation was found between
DNA methyltransferase 1 overexpression and Scarff-Bloom-Richardson histologic grade III (P = .01).
DNA methyltransferase 3a overexpression was significantly associated with menopausal status (P = .01), Scarff-Bloom-Richardson histologic grade III (P = .0001),
estrogen (P = .04) and
progesterone (P = .007) receptor negativity, and HER2 overexpression (P = .004). However,
DNA methyltransferase 3a overexpression was found less frequently in the
luminal A intrinsic
breast cancer subtype (9.7%) than in
luminal B (53%), HER2 (41%), and triple-negative (50%) subtypes (P = .001).
DNA methyltransferase 3b overexpression shows significant correlation with promoter hypermethylation of BRCA1 (P = .03) and RASSFA1 (P = .04) and with the hypermethylator phenotype (more than 4 methylated genes, P = .01). These data suggest that overexpression of various
DNA methyltransferases might represent a critical event responsible for the epigenetic inactivation of multiple tumor suppressor genes, leading to the development of aggressive forms of sporadic
breast cancer.