2992 - Partial Breast Irradiation Following Lumpectomy without Surgical Axillary Evaluation

03:00pm - 04:00pm PT

Hall F

Screen: 11

POSTER

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):

The contemporary management of early stage breast cancer increasingly omits surgical axillary nodal staging. While the studies defining excellent outcomes in the absence of sentinel lymph node biopsy (SLNB) or axillary lymph node dissection (ALND) relied overwhelmingly on adjuvant whole breast irradiation (WBI), little data exist in this context regarding the feasibility of partial breast irradiation (PBI). We evaluated oncologic outcomes for breast cancer patients managed with breast conserving surgery and PBI, without surgical axillary evaluation.

Materials/Methods:

Using a prospectively maintained institutional database, we ascertained all breast cancer patients treated from 2014 to 2022 with breast conservation and PBI, but who did not undergo SLNB or ALND. Salient clinicopathologic and treatment parameters were collected. Primary endpoints included local, regional and distant recurrence rates, in addition to contralateral recurrences and overall survival (OS). Cumulative incidences of each event type were estimated with other events and death as competing risks. OS was estimated using the Kaplan-Meier method. All statistical analyses were performed in R version 4.4.1.

Results:

The cohort comprised 78 patients (median age 75 years; range 50-91), with 28% aged =70 years, and 13% =65 years. Predominant pathologic characteristics included: T1 disease (86%), invasive ductal carcinoma (79%), low-intermediate grade tumors (76%), absence of lymphovascular invasion (92%), estrogen receptor positivity (92%), and HER2 negativity (91%). All were clinically node negative by physical exam, with only one patient undergoing axillary ultrasound. Most had =2 mm resection margins (89%) and received endocrine therapy (77%), while a small minority received chemotherapy (3%).

At a median 40-months of follow-up, we observed no instances of local, regional, or distant recurrence. A single contralateral recurrence was observed (4-year cumulative incidence rate = 1.3%; 95% CI 0.1-6.3), as were two unrelated deaths that occurred at 4.2 and 6.4 years following diagnosis.

Conclusion:

We observed excellent oncologic outcomes among patients with clinically node negative breast cancer who underwent lumpectomy and PBI without surgical axillary nodal evaluation. Longer term follow-up among larger cohorts will be needed to validate this paradigm. These findings suggest that PBI may be a feasible approach in this population, and that WBI need not be mandated in all cases where axillary nodal staging is omitted.