Sep 30

SS 31 - Breast Cancer 3: Refining Radiation in Early-Stage Breast Cancer: Personalization, Precision, and De-escalation

283 - Prognostic Significance of Lymph Node Tumor Deposit Size in Early-Stage Breast Cancer

08:40am - 08:50am PT

Room 24

Presenter(s)

Diana Roth O’Brien, MD, MPH - Memorial Sloan Kettering Cancer Center, New York, NY

D. A. Roth O’Brien¹, L. A. Boe², B. A. Mueller¹, G. Montagna³, J. J. Cuaron¹, I. J. Choi¹, M. B. Bernstein⁴, B. McCormick¹, S. N. Powell¹, A. J. Khan⁴, and L. Z. Braunstein⁴; ¹Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, ²Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, NY, ³Breast Service, Department of Surgery, Memorial Sloan Kettering Cancer Center, New York, NY, ⁴Memorial Sloan Kettering Cancer Center, New York, NY

Purpose/Objective(s):

Breast cancer nodal staging relies primarily on the anatomic location and number of involved lymph nodes (LNs). This study investigated the prognostic value of LN tumor deposit size, focusing on patients with single-node involvement to isolate size-specific effects.

Materials/Methods:

Using a prospectively-maintained institutional database, we identified breast cancer patients treated 1992-2023 with a single involved LN (ie. =pN1), none of whom received neoadjuvant therapy. Nodal involvement was classified as pN0, pN0i+, pN1mic, or pN1a subdivided into 5mm increments. Primary endpoints included locoregional recurrence (LRR), distant metastasis (DM), disease-free survival (DFS), and overall survival (OS). Statistical analyses employed competing risk methodology for LRR and DM, Kaplan-Meier estimation for survival outcomes, and multivariable regression modeling.

Results:

The study cohort included 14156 patients (median age 56.5), of which 88% had pN0 disease, 2% pN0i+, 4% pN1mic, and the remaining 6% harbored pN1a disease with a single macrometastasis. 72% of patients had breast conserving surgery and the majority (93%) underwent sentinel lymph node biopsy. Most patients (91%) had estrogen receptor positive (ER+) disease, with 8% HER2+. 85% received endocrine therapy (ET), 36% chemotherapy, and 66% radiotherapy (RT). Median time to follow up or death was 73 months.

6-year DFS was 88% and differed significantly by LN tumor size: 89% for pN0, 86% for pN0i+, 82% for pN1mic, 82% for pN1a with a deposit of 2.1-5mm, 84% for 5.1-10mm, 83% for 10.1-15mm, 74% for 15.1-20mm, and 77% for >20mm (p< 0.001). These differences were driven largely by risk of DM with increasing deposit size: 6-year DM rate of 3.8% for pN0, 6.0% for pN0(i+), 9.5% for pN1mic, 8.7% for pN1a with a deposit of 2.1-5mm, 8.7% for 5.1-10mm, 8.7% for 10.1-15mm, 17% for 15.1-20mm, and 21% for >20mm.

Conversely, among 757 LRRs, incidence of LRR did not differ by node size (p=0.6). On multivariable analysis (MVA), age, mastectomy, primary tumor size, receipt of ET, and receipt of RT were associated with LRR (p< 0.001), however LN tumor size was not (p=0.7).

We observed 898 deaths over the follow up period, for a 6-year OS of 95% that differed significantly by LN deposit size: 6-year OS was 96% for those with pN0 disease, 94% for pN0(i+), 92% for pN1mic, 89% for a single deposit of 2.1-5mm, 93% for 5.1-10mm, 93% for 10.1-15mm, 84% for 15.1-20mm, and 88% for a deposit of >20mm (p<0.001). LN tumor size remained associated with OS on MVA (HR = 1.03 per mm; p<0.001).

Conclusion:

In early-stage breast cancer with a single involved LN, increasing nodal tumor size is adversely associated with DM, DFS and OS, but not with LRR, suggesting that LN tumor size may serve as a surrogate for systemic disease burden rather than as a locoregional risk factor. This distinction has important implications, potentially informing regional nodal irradiation and systemic therapy decisions.