Little is known about epigenetic silencing of genes by promoter hypermethylation in lobular breast cancers. The promoter methylation status of 5 cancer-related genes (RASSF1A, HIN-1, RAR-beta, Cyclin D2 and Twist) was evaluated in 2 types of lobular cancers, in situ (LCIS) and invasive lobular carcinomas (ILC) (n = 32), and compared to ductal in situ (DCIS) and invasive (IDC) breast cancers (n = 71). By using methylation-specific PCR (MSP), 100% of ILC and 69% of LCIS cases were found to have 1 or more hypermethylated genes among the panel of 5 genes (compared to 100% IDC and 95% of DCIS). Two or more hypermethylated genes were detected per tumor in 79% of invasive and 61% of in situ lobular carcinomas compared to 81% of IDC and 77% of DCIS. By contrast, DNA from nearly all normal reduction mammoplasty tissues (n = 8) was unmethylated for the 5 genes. The methylation profiles of lobular vs. ductal carcinomas with respect to RASSF1A, Cyclin D2, RARbeta, and Hin-1 genes were similar, suggesting that gene silencing by promoter hypermethylation is likely to be important in both groups of diseases. Distinctly different, Twist was hyper- methylated less often in ILC (16%, 3/19 cases) than in IDC (56%, 15/27 cases) (p = 0.01). These results suggest that these 2 types of tumors share many common methylation patterns and some molecular differences. Additional studies might lend further understanding into the etiology and clinical behavior of this tumor type.
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