Effectiveness of Postoperative Irradiation in Patients with cN0 Early Breast Cancer Treated with Sentinel Lymph Node Surgery.

To evaluate the effectiveness of postoperative irradiation (POI) for patients with cN0 early breast cancer, we retrospectively analyzed the cases of 650 consecutive breast cancer patients who underwent sentinel lymph node (SLN)-guided surgery (2005-2022) at our hospital. In this cohort, 53% (278/521) of the patients who underwent breast conservative surgery (BCS) and 96% (124/129) of those treated with mastectomy did not receive POI. The patients who underwent BCS were treated with POI using opposing tangential field irradiation. A false negative (FN) SLN was retrospectively defined as a negative metastasis in SLN plus positive recurrence in the axillary lymph nodes. Recurrence was detected in 83 patients. A logistic regression analysis revealed that the nuclear grade (odds ratio [OR] 1.69), POI (OR 0.41), and postoperative hormone therapy (OR 0.40) were each significantly related to recurrence. The 26.1% (12/46) FN rate of the non-POI patients decreased to 5.8% (1/17) compared to those treated with POI. The rate of axillary recurrence was significantly lower in the POI group (0.4%) versus the non-POI group (2.7%) (p=0.0355). The rate of locoregional recurrence was also significantly lower in the POI group (2.0%) versus the non-POI group (13.4%) (p<0.0001). No significant difference was observed in the rate of distant recurrence between the POI (4.0%) and non-POI (3.3%) (p=0.831) groups. These results indicated that the postoperative opposing tangential field irradiation of conserved breast tissue inhibited recurrence in the axillary lymph nodes.