Abstract P3-12-23: Utilization and survival benefit of radiation therapy among hormone receptor positive breast cancer patients with recurrence score from Oncotype DX testing
Authors: Zhang L , Hsieh M-C , Petkov VI , Wu X-C , Yu Q 
Published: May 2019

Abstract
Background: Radiation therapy (RT) improves survival of breast cancer (BC) patients receiving the lumpectomy. Oncotype DX, a 21-gene Recurrence Score (RS) assay, has been validated to predict the risk of recurrence and chemotherapy benefit for hormone receptor positive (HR+) BC without metastatic lymph nodes (PN0). With increasing use of Oncotype DX, it is unclear if the utilization and survival benefit of RT vary by RS in clinical practice. This study aimed to 1) examine if the RS from Oncotype DX testing influences RT utilization among HR+ BC patients with PN0 who received lumpectomy; and 2) investigate if RT is associated with better cause-specific survival (CSS) and overall survival (OS) among patients stratified by the low, intermediate, and high RS.
Methods: Data from Genomic Health Inc., the sole Oncotype DX testing provider in the U.S., was linked with routinely collected data from 17 SEER registries. Women who were diagnosed with PN0 and HR+ BC in 2004-2015, received the lumpectomy, and had RS from Oncotype DX testing were included. Patients who had multiple tumors, received RT before or within surgery, or had less than 2 months follow-up were excluded. Patients diagnosed in 2004-2014 and followed through the end of 2015 were included in the survival analysis. RS was categorized into low (&lt;18), intermediate (18-30), and high (&gt;30). RT was categorized into yes, no or unknown. Multivariable logistic regression was applied to examine the association between RS and RT utilization. To compare survival differences, patients receiving RT and patients having no or unknown RT were matched on propensity score, which was calculated based on diagnosis year, age, race, marital status, tumor size, grade, number of lymph nodes examined, chemotherapy, and participating state. Stratified Cox proportional hazards models were used to compare CSS and OS between two matched groups. Proportional hazard assumption was evaluated.
Results: Out of 48,615 patients, 56.8% had low, 36.1% had intermediate, and 7.1% had high RS; 84.5% received RT (86.6%, 82.8%, and 76.4% in low, intermediate, and high RS patients, respectively; P &lt; 0.0001). After adjusting for covariates, patients with intermediate (odds ratio [OR] 0.75; 95% CI 0.71-0.79; P &lt; 0.0001) and high RS (OR 0.53; 95% CI 0.47-0.59; P &lt; 0.0001) were less likely to receive RT than patients with low RS. Among patients with low or intermediate RS, having no or unknown RT was associated with worse CSS (low RS: hazard ratio [HR] 6.00, 95% CI 1.77-20.37, P = 0.004; intermediate RS: HR 2.12, 95% CI 1.19-3.77, P = 0.01) and OS (low RS: HR 2.29, 95% CI 1.56-3.35, P &lt; 0.0001; intermediate RS: HR 2.22, 95% CI: 1.54-3.21, P &lt; 0.0001). RT utilization was not significantly associated with CSS or OS among patients with high RS.
Conclusions: Among HR+, PN0 BC patients receiving the lumpectomy, lower RS was associated with higher RT utilization. RT was associated with better CSS and OS among patients with low or intermediate RS. Among patients with high RS, no association between RT and survival was observed.
Citation Format: Zhang L, Hsieh M-C, Petkov VI, Wu X-C, Yu Q. Utilization and survival benefit of radiation therapy among hormone receptor positive breast cancer patients with recurrence score from Oncotype DX testing [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-12-23.