This study investigated methylation status of seven imprinted differentially methylated regions—PLAGL1/ZAC1, H19-ICR1, IGF2-DMR2, KvDMR-ICR2, RB1, SNRPN-DMR1 and PEG3—in blood samples from 189 women with the most common type of invasive breast cancer (invasive ductal carcinoma—IDC), 41 women with in situ breast cancer (ductal carcinoma in situ—DCIS) and 363 matched disease-free controls. The gene discussed is RB1; the disease is ductal breast carcinoma in situ.