2804 - Evaluating the Effects of Regional Nodal Radiation in Node-Positive Triple-Negative Breast Cancer: Identifying the Beneficiaries

Purpose/Objective(s):

Triple-negative breast cancer (TNBC) is an aggressive subtype associated with a high risk of locoregional and distant failure, particularly in node-positive disease. While regional nodal irradiation (RNI) improves outcomes in selected breast cancer populations, its role in TNBC with adverse features such as extracapsular extension (ENE), high nodal burden is incompletely defined. The interplay between the extent of axillary surgery, RNI, and failure patterns is insufficiently defined. This retrospective study evaluated the impact of RNI on survival outcomes and failure patterns in node positive TNBC cohort.

Materials/Methods:

Data collected included nodal burden, ENE, response to neoadjuvant chemotherapy (NACT), type of breast surgery, extent of axillary surgery (sentinel lymph node biopsy (SLNB) vs axillary lymph node dissection (ALND), radiotherapy fields (axillary, supraclavicular, and internal mammary), and recurrence patterns [within irradiated fields (in-field) or outside irradiated regions (out of field)]. Overall survival (OS) and progression-free survival (PFS) were estimated using the Kaplan-Meier method and compared with the log-rank test

Results:

101 patients, median age 45 years were included (RNI: 76; no RNI: 25). Clinicopathologic characteristics were balanced in both groups. Sixty-one patients received breast -conserving surgery (RNI: 43; no RNI: 18) and 39 mastectomy (RNI: 32; no RNI: 7).Neoadjuvant chemotherapy was given to 52 (51.5%) patients (RNI: 47; no RNI: 5) 29 achieving complete response (RNI: 25; no RNI = 4).

Among 64 patients evaluable for recurrence (RNI n = 53; no RNI n = 11), locoregional recurrence occurred in 5 patients (8%), 3 in RNI , 2 no RNI. Regional nodal failures (n=4) involved axilla (n = 2, both in-field after RNI), supraclavicular/internal mammary (n = 2, both in no-RNI).

Among patients with SLNB (n = 15), 2 (13%) developed recurrences in supraclavicular/internal mammary regions, outside irradiated fields. After ALND I – II (n = 24), one axillary recurrence (4%) occurred with no axillary RT, while no nodal failures were seen after ALND I – III with axillary irradiation. Distant metastases (brain, skeletal) occurred only in ALND patients without axillary RT. Median time to first recurrence was longer with RNI (44 months) than with no RNI (15 months).

Grade =2 toxicities were infrequent and comparable. With a median follow-up of 98 months, median OS was 114 months with RNI versus 76 months without RNI (log-rank p = 0.072). Median PFS was significantly improved with RNI (98 vs 74 months; log-rank p = 0.025). Long-term survival estimates at 3, 5, and 7 years consistently favoured the RNI group.

Conclusion:

In this high-risk node-positive TNBC cohort, RNI reduced locoregional failures despite axillary surgery and was associated with significantly improved PFS and favourable long-term outcomes, with a trend toward improved OS.