IL21R and breast cancer: The methylation levels of each CpG site in the IL21R amplicon significantly differed between the ER-positive and ER-negative groups of BC patients (CpG_2: p-value = 0.026, CpG_3: p-value = 2.42E–04, CpG_4: p-value = 2.00E–06, CpG_5: p-value = 7.53E–08, CpG_6: p-value = 5.30E–05; Table 3).