ESTRO 2024 - Abstract Book

S619

Clinical - Breast

ESTRO 2024

Purpose/Objective:

The role of postoperative radiotherapy in breast cancer patients has long been established and widely practiced. Studies have shown that regional nodal irradiation (RNI) improves outcomes in patients with positive lymph nodes. During recent years neoadjuvant chemotherapy has become the standard treatment for patients with positive lymph nodes. Nevertheless, the radiotherapy (RT) field is controversial. Also, the RT field for different molecular subtypes are still controversial. Therefore, in this study, we analyzed the clinical outcomes according to the field of radiotherapy in patients who transitioned from cN1 to ypN0 stage.

Material/Methods:

This study included breast cancer patients who received neoadjuvant chemotherapy and postoperative radiotherapy for breast cancer from 2007 to 2018, and who converted from cN1 stage to ypN0 stage. For HER2 positive patients, patients who did not receive HER2 targeted therapy were excluded. Patients were divided into three groups according to radiotherapy coverage: Whole breast or chest wall alone (WBI), whole breast or chest wall + axillary node area + supraclavicular lymph node area (AXL+SCL), whole breast or chest wall + axillary node area + SCL + elective IMN area (full RNI), and analyzed for overall survival (OS), disease free survival (DFS), loco-regional recurrence free survival (LRRFS) and toxicity.

Results:

Of the 570 total patients, 170 were in the WBI group, 328 in the AXL+SCL group, 71 in the full-RNI group. The median follow-up period was 7.19 years. HER-2 negative patients received chemotherapy that includes doxorubicin and docetaxel, and HER-2 positive patients received HER2 targeted treatment. For all patients, 5-year OS was 98.3%, DFS was 90.8%, and LRRFS was 97.7%. The differences in OS, DFS, and LRRFS by RT field were not significant, and neither were the differences by subtype. In the subgroup analysis of Luminal A, Luminal B, HER2-enriched, and TNBC types, no differences were observed in OS, DFS, and LRRFS by RT field. Univariate and multivariate analyzes also showed that RT field and subtype were not correlated with OS, DFS, and LRRFS.

Toxicity was analyzed for lymphedema and symptomatic pneumonitis. Symptomatic pneumonitis was not related to the RT field, but lymphedema tended to occur more often as the RT field became wider.