Abstract P3-07-05: Oncotype Dx use and its relationship with chemotherapy administration in the general population
Authors: Chavez-MacGregor Mariana , Niu Jiangong , Smith Benjamin , Zhao Hui , Buchholz Thomas A , Giordano Sharon H 
Published: May 2015

Background: Oncotype Dx is a 21-gene assay performed in paraffin-embedded tumor tissue. This test is used to assist in estimating the likelihood of recurrence and the benefit from chemotherapy in patients with hormone receptor (HR)-positive, node-negative breast cancer. One of he purported benefits of this assay is that by identifying low risk patients, Oncotype Dx use will be associated with a decrease in chemotherapy use among those patients less likely to benefit from it. In this study we sought to describe the utilization patterns of Oncotype Dx and its relationship with the use of adjuvant chemotherapy in a large population-based study.

Methods: We identified 112,522 patients younger than 65 years old diagnosed with early stage breast cancer between 2004-2012 in the MarketScan database. Standard algorithms were used to identify our cohort and HR-positivity was defined according to prescription information. A total of 34,245 patients older that 66 and diagnosed with early stage breast cancer between 2006-2009 were identified in the SEER-Medicare database. Descriptive statistics were used as well as logistic regression models to estimate the impact of Oncotype Dx testing on adjuvant chemotherapy administration.

Results: In the cohort of young patients (&lt;65 years old), 13.9% (n=15,643) underwent Oncotype Dx testing. Among those with HR-positive disease, the percentage use was 71.8%. The use of Oncotype Dx increased according to age and year of diagnosis (p&lt;.001), going from 0.11% in 2005 to 21.9% in 2011. In the multivariable model, Oncotype Dx testing was associated with a reduction in the use of adjuvant chemotherapy (OR 0.78; 95% CI 0.75-0.81).

Among the older patients (≥66 years old), 11.35% (n=3,017) underwent Oncotype Dx testing. Utilization was associated with younger age, histological grade, educational level, marital status, geographic location and comorbidities (p&lt;0.001). Oncotype Dx use increased according to year of diagnosis going from 3.7% in 2006 to 14.11% in 2009 (p&lt;0.001). Among the patients with Oncotype Dx test, 85.5% had node-negative disease. In the multivariable model Oncotype Dx testing was not associated with a statistically significant reduction in the use of chemotherapy (OR 0.95; 95% CI 0.86-1.06)

Conclusions: The use of Oncotype Dx in clinical practice is common, with an increase use in more recent years. Utilization was determined by patient-related characteristics. Among younger patients Oncotype Dx testing was associated with a reduction in the use of adjuvant chemotherapy, but this decrease was not observed among those ≥66 years old. It is possible that this discordance is related to comorbidities and the fact that older patients are less likely to be considered candidates for chemotherapy.

Citation Format: Mariana Chavez-MacGregor, Jiangong Niu, Benjamin Smith, Hui Zhao, Thomas A Buchholz, Sharon H Giordano. Oncotype Dx use and its relationship with chemotherapy administration in the general population [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-07-05.