The methylation levels of the 15 genes MAST1, PRDM14, ZNF177, DNM2, SSH1, AP2M1, CACNA1E, CPEB4, DLGAP2, CCDC181, GCM2, ITPRIPL1, POM121L2, KCNQ1, and TIMP3 were studied by modified MS–HRM in small malignant breast tumor (test set, n = 48), fibroadenoma (n = 24), and healthy tissue from patients with fibroadenoma (n = 24). This evidence concerns the gene MAST1 and breast cancer.