Methylation Patterns of Tumor Suppressor Genes in Breast DCIS Tumors

ABSTRACT

PURPOSE: The methylation of tumor suppressor genes has been implicated in the development of breast cancer. However, the role of methylation in the progression of cancer is still unclear. In this study, the methylation stati of nine tumor suppressor genes (p14, p16, DAPK, E-cadherin, RASSF1 alpha, TWIST, RAR beta, HIN-1, cyclin D2) in normal, benign, DCIS and invasive cancer tissues were examined, and the methylation patterns in DCIS and hypermethylated genes investigated to see if a change in the methylation status would lead to the development of cancer and progression to an invasive tumor. METHODS: A total of 96 patients, who underwent surgery between March 2003 and March 2005, were retrospectively studied. DNA was extracted from tumor tissues, and the samples examined for aberrant hypermethylation using methylation-specific PCR (MSP). RESULTS: The total number of methylated genes in each tissue type (normal tissues; 2.97+/-1.74, benign tumors; 4.36+/-1.42, DCIS; 5.73+/-1.35, invasive cancers; 5.42+/-2.05) increased with tumor progression (P<0.001). In benign tumors, HIN-1 (83%) was the most frequently methylated gene, but in DCIS, p14 (100%), RASSF (100%) and TWIST (91%) were frequently methylated. In invasive cancer, RAR beta (60%) and p16 (37%) were frequently methylated compared to the other tissue types. In a multivariate study, TWIST was commonly hypermethylated in DCIS and invasive cancer; whereas, RAR beta and p14 were frequently independently hypermethylated in invasive cancers. CONCLUSION: Methylation induced gene silencing appears to affect multiple genes in breast tissues, which increases with cancer progression. TWIST was hypermethylated in both DCIS and invasive cancers; therefore, it was concluded that methylation of the TWIST promoter may be an early event in the development of breast cancer. The hypermethylations of RAR beta and p16 are useful marker for the progression of a DCIS lesion to invasive cancer. The methylation patterns of tumor suppressor genes in DCIS were similar to those found in invasive cancer, but also showed intermediate levels of methylation between benign tumors and invasive cancers.