MKI67 and breast carcinoma: Unexpectedly, irrespective of the age at irradiation, the Ki-67 index was significantly correlated with the PR index in HR-positive mammary carcinomas from parous rats (Fig. 4c; all parous groups combined, R = 0.57, p = 0.0004; No-IR only, p = 0.18; IR-3W only, p = 0.0095; IR-7W only, p = 0.0029), but not in virgin rats (Fig. 4c).