Examining Rural-Urban Differences in Genomic Testing Use for Breast Cancer in Idaho, 2013-2022

Oncotype DX RS is a 21-gene assay that can be used to guide treatment decisions regarding adjuvant chemotherapy for women diagnosed with early-stage, estrogen receptor positive, human epidermal growth factor receptor 2 negative (ER+/HER2-) breast cancer. Despite inclusion in clinical guidelines, research suggests that gene expression profile (GEP) testing is underutilized in the United States-particularly among rural patients. Oncotype DX RS testing has not been evaluated in Idaho, a largely rural state.

We used Idaho central cancer registry data in generalized estimating equations to determine if rural Idaho residents diagnosed with early-stage breast cancer during 2013-2022 were less likely to receive GEP testing than their urban counterparts.

Of 6,984 eligible tumors, 55.2% (433/785) linked to GEP testing in 2022, up from 36.8% (212/576) in 2013. Although patient rurality was not associated with GEP testing (adjusted RR = 0.97, 95% CI: 0.85-1.11), we noted a high degree of variability by patient county of residence.

Contrary to prior research, our results show no difference in GEP testing among breast cancer patients by rural residency.

The rural-urban gap in accessing personalized medicine for early-stage breast cancer may be closing, but patterns of care remain highly variable across geography. The relationship between patterns of care and residence merits further investigation to improve survivor quality of life.