Abstract
To better understand breast cancer etiology and progression, we explored the association between promoter methylation status of three breast cancer-related genes (BRCA1, APC, and p16) and survival in a large cohort of women with breast cancer. About 800 archived tumor tissues were collected from women diagnosed with a first primary invasive or in situ breast cancer in 1996-1997. The vital status of the participants was followed through the end of year 2005 with a mean follow-up time of 8.0 years. Promoter methylation was assessed by methylation-specific PCR (for BRCA1) and MethyLight (for APC and p16). The association of promoter methylation and breast cancer mortality was evaluated by Cox-proportional hazards models. Methylated promoters were found in 59.0, 48.4, and 3.6% of the tumor samples for BRCA1, APC, and p16, respectively. Breast cancer-specific mortality was strongly associated with promoter methylation of p16 [HR and 95% CI: 3.53 (1.83-6.78)], whereas the associations with of BRCA1 and APC were less pronounced [HR and 95% CI: 1.81 (1.18-2.78) and 1.46 (0.98-2.17), respectively]. Similar associations were observed with all-cause mortality. As the number of methylated genes increased, the risk of breast cancer-specific mortality also increased in a dose-dependent manner (P, trend = 0.01). Importantly, even with our results stratified by hormone receptor status, promoter methylation of the three genes remained predictive of mortality. Our results suggest that promoter methylation could be promising epigenetic markers to be considered for breast cancer survival.