Adjuvant radiotherapy is indicated in patients with node spread of breast cancer, even after a mastectomy. The benefit is larger in patients with more than 3 lymph node involvement. Patients with risk factors such as young age, high grade of cancer or larger tumour also benefit from radiotherapy. In recent times, the uptake of neoadjuvant chemotherapy has increased in patients with breast cancer. Neoadjuvant chemotherapy is sometimes administered before surgery with the goal of shrinking tumors.

The necessity of adjuvant radiotherapy after neoadjuvant chemotherapy for breast cancer depends on various factors. This is especially important in patients with triple negative or HER2-enriched breast cancers as many of these patients can get complete response with chemotherapy or targeted therapy alone. As such, a few large clinical trials are ongoing to investigate if patients with complete response after chemotherapy still require radiotherapy.

The NRG Oncology/NSABP B-51 trial presented at the 2023 San Antonio Breast Cancer Symposium is one such study. It focused on patients whose breast cancer changed from lymph node positive to lymph node negative. The trial studied whether skipping regional nodal irradiation (RNI) increased the risk of relapse or death five years after surgery. The study involved 1,641 patients with lymph node–positive, non-metastatic breast cancer. It found that those who became lymph node–negative after chemotherapy could safely omit adjuvant RNI without an increased risk. The outcomes were similar for patients who received RNI and those who did not. This suggests that treating regional lymph nodes with neoadjuvant chemotherapy allows some patients to skip RNI.

However, the study acknowledges the need for longer results to strengthen the analysis.

For now, patients with clinical breast tumours up to stage cT3 ( i.e skin was not involved without chest wall invasion) and N1 ( no neck or internal mammary nodes) who achieve complete response afterchemotherapy may discuss skipping ofradiotherapy. However, patients with risk factors should have a discussion with their treating doctors.

Patients who do not have complete response to chemotherapy will require adjuvant radiotherapy after surgery to ensure optimal local control of tumour.