Adoption of gene expression profile testing and association with use of chemotherapy among women with breast cancer

Abstract

Purpose: Gene expression profile (GEP) testing is a relatively new technology that offers the potential of personalized medicine to patients, yet little is known about its adoption into routine practice. One of the first commercially available GEP tests, a 21-gene profile, was developed to estimate the benefit of adjuvant chemotherapy for hormone receptor-positive breast cancer (HR-positive BC).

Patients and methods: By using a prospective registry data set outlining the routine care provided to women diagnosed from 2006 to 2008 with HR-positive BC at 17 comprehensive and community-based cancer centers, we assessed GEP test adoption and the association between testing and chemotherapy use.

Results: Of 7,375 women, 20.4% had GEP testing and 50.2% received chemotherapy. Over time, testing increased (14.7% in 2006 to 27.5% in 2008; P < .01) and use of chemotherapy decreased (53.9% in 2006 to 47.0% in 2008; P < .01). Characteristics independently associated with lower odds of testing included African American versus white race (odds ratio [OR], 0.70; 95% CI, 0.54 to 0.92) and high school or less versus more than high school education (OR, 0.63; 95% CI, 0.52 to 0.76). Overall, testing was associated with lower odds of chemotherapy use (OR, 0.70; 95% CI, 0.62 to 0.80). Stratified analyses demonstrated that for small, node-negative cancers, testing was associated with higher odds of chemotherapy use (OR, 11.13; 95% CI, 5.39 to 22.99), whereas for node-positive and large node-negative cancers, testing was associated with lower odds of chemotherapy use (OR, 0.11; 95% CI, 0.07 to 0.17).

Conclusion: There has been a progressive increase in use of this GEP test and an associated shift in the characteristics of and overall reduction in the proportion of women with HR-positive BC receiving adjuvant chemotherapy.

Fig 1.

(A) Temporal trends in gene expression profile (GEP) testing and chemotherapy use for all patients, (B) stratified by nodal (N) status, and (C) by cancer center type. Patients with hormone receptor–positive stage I to III breast cancer were diagnosed from 2006 to 2008. Mantel-Haenszel χ² P < .001 for all trends except chemotherapy use at community-based cancer centers (P = .74). There were fewer patients from community-based cancer centers in 2006 than in subsequent years because these centers started contributing patients to the data set part way into 2006. Community, community-based cancer center; Comprehensive, comprehensive cancer center.

Fig 2.

(A) Distribution of gene expression profile (GEP) test results for this study and previously published results and (B) for this study stratified by clinically based risk. Cutoffs for low- (< 18), intermediate- (18–30), and high- (≥ 31) risk GEP test results were previously defined as part of the test development process.^– Treatment recommendation groups are based on clinical characteristics, as derived from National Comprehensive Cancer Network (NCCN) clinical practice guidelines. Results from this study include 95% CIs. Three of 1,454 patients with a known GEP result could not be assigned to a clinical risk stratum because of missing pathology data. NSABP, National Surgical Adjuvant Breast and Bowel Project; SWOG, Southwest Oncology Group.