In addition, methylation levels of each CpG site in the IL21R amplicon were significantly lower in the triple-negative group compared to the non-triple-negative group of BC patients (CpG_2: p-value = 0.014, CpG_3: p-value = 0.001, CpG_4: p-value = 0.002, CpG_5: p-value = 0.001, CpG_6: p-value = 0.002; Table 3) Moreover, compared with the HER2-negative group, only CpG_5 showed significantly decreased methylation levels in the HER2-positive group (p-value = 0.024; Table 3). The gene discussed is ERBB2; the disease is breast cancer.