Detection of any level of aberrant methylation (PMR>0) resulted in a specificity for detecting breast cancer of 95% for APC, 100% for RASSF1A and 89.5% for ESR1. The frequency of methylation in serum DNA of APC and RASSF1A was significantly higher among women with breast cancer as compared with controls: APC, 29 versus 5% (P=0.03) and RASSF1A, 35 versus 0% (P=0.002). The gene discussed is RASSF1; the disease is breast cancer.