3002 - Is Partial Breast Irradiation Effective for Early-Stage Breast Cancer Patients with High-Risk Molecular Recurrence Scores?

03:00pm - 04:00pm PT

Hall F

Screen: 12

POSTER

Presenter(s)

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

A. Terry¹, L. A. Boe², K. R. Pawloski³, D. A. Roth O’Brien⁴, B. A. Mueller⁴, I. J. Choi⁴, S. N. Powell⁴, A. J. Khan⁴, L. Kirstein³, and L. Z. Braunstein¹; ¹Memorial 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, ⁴Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY

Purpose/Objective(s):

Partial breast irradiation (PBI) is a suitable alternative to whole breast irradiation (WBI) for many forms of low-risk, early-stage breast cancer following lumpectomy. Molecular risk scores, such as the Oncotype DX recurrence score (ODX RS), are increasingly guiding systemic treatment decisions. However, their implementation for radiotherapy (RT) decision making remains investigational, and it is currently unclear whether a high ODX RS should preclude the use of PBI. We evaluated oncologic outcomes among patients with high-risk ODX RS treated with either PBI or WBI.

Materials/Methods:

Patients were ascertained from a prospectively maintained institutional database. Patients with an ODX RS > 25 who underwent breast conservation followed by PBI or WBI were included. Propensity score matching based on multiple clinicopathologic features generated comparable PBI and WBI cohorts in 1:5 fashion. We estimated the incidence of local recurrence (LR) in each group.

Results:

We identified 968 patients with an ODX RS > 25 who were treated with adjuvant RT, with median age of 59 years and a median 5.3 years of follow-up. Most patients had T1 disease (76.5%) and received adjuvant chemotherapy (86%) and endocrine therapy (95%). In a propensity matched cohort analysis that included all 28 patients who received PBI matched to 140 who received WBI, we observed three LR events among those receiving PBI (only one of which was in the same quadrant as the primary lesion) and five events among those receiving WBI. The 72-month cumulative incidence of local recurrence was 7.9% (95% CI: 1.3%-23%) for PBI compared to 4.8% (95% CI: 1.6%-11%) for WBI (p=0.6).

Conclusion:

In this cohort of patients with high ODX RS, few local recurrences were observed, and no statistically significant difference in local recurrence incidence was identified between PBI and WBI. While these findings suggest that PBI may be considered in carefully-selected high-genomic-risk patients, larger prospective studies are needed to definitively establish the safety of this approach.