REGIONAL nodal irradiation in breast cancer showed low recurrence rates after nodal pCR, even when residual breast disease remained.
Regional Nodal Irradiation After Nodal pCR
Regional nodal irradiation remains an important question in women with cT1–3N1 breast cancer who receive neoadjuvant chemotherapy and achieve a pathologic complete response in the axillary nodes. In this single institution study, investigators examined whether outcomes differed between patients who also achieved a breast pathologic complete response and those with residual disease in the breast.
The analysis included 124 patients treated between 2010 and 2021 who had biopsy proven nodal disease at diagnosis, completed neoadjuvant chemotherapy, and achieved nodal pCR. Patients underwent either breast conserving surgery or mastectomy. Among this group, 72 patients, representing 58%, also achieved a breast pCR.
Breast Response and Disease Free Survival
At a median follow up of 5 years, outcomes were favorable overall. The 5-year disease free survival rate was 92.3%, and rates of local recurrence or distant metastasis were low across the cohort. Patients without a breast pCR had a numerically higher recurrence rate than those with a breast pCR, at 12% versus 4.2%. However, this difference was not statistically significant.
These findings are notable because the breast pCR rate in this study was lower than the rate reported in the B51 trial population. The data suggest that patients with nodal pCR do not uniformly achieve a complete response in the breast, even when nodal clearance has occurred after neoadjuvant chemotherapy.
HER2 Status Linked to Breast pCR
On multivariate analysis, HER2 positive breast cancer was strongly associated with a higher likelihood of breast pCR compared with HER2 negative disease. This finding may help explain which patients are more likely to achieve complete eradication of disease in both the nodes and the breast after systemic treatment.
The authors noted that patients with ER/PR positive and HER2 negative disease may be less likely to achieve breast pCR and may also recur later, which limits conclusions from shorter follow up. Although no significant disease-free survival difference was seen in this cohort, the study highlights an important subgroup for future evaluation.
Overall, the findings suggest that regional nodal irradiation decisions should not rely on nodal pCR alone. Additional research is needed to clarify whether women with residual breast disease after nodal pCR derive added benefit from regional nodal irradiation, particularly in biologic subtypes less likely to achieve breast pCR.
Reference
Hardy-Abeloos C et al. Effectiveness of Regional Nodal Irradiation in Women with a Pathologic Complete Response in the Nodes After Neoadjuvant Chemotherapy with Residual Disease in the Breast. Pract Radiat Oncol. 2025;doi:10.1016/j.prro.2025.09.001.
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