Surgeon and medical oncologist peer network effects on the uptake of the 21‐gene breast cancer recurrence score assay

BACKGROUND: Drivers behind the adoption of gene expression profiling in breast cancer oncology have been shown to include exposure to physician colleagues’ use of a given genomic test. We examined adoption of the Oncotype DX 21‐gene breast cancer recurrence score assay (ODX) in the United States after its incorporation into clinical guidelines. The influence of patient‐sharing ties and co‐location with prior adopters and the role of these potential exposures across medical specialties on peers’ adoption of the test were examined. METHODS: We conducted a retrospective cohort study of women with incident breast cancer using a 100% sample of fee‐for‐service Medicare enrollee claims over 2008–2011. Peer networks connecting medical oncologists and surgeons treating these patients were constructed using patient‐sharing and geographic co‐location. The impact of peer connections on the adoption of ODX by physicians and testing of patients was modeled with multivariable hierarchical regression. RESULTS: Altogether, 156,229 women identified with incident breast cancer met criteria for cohort inclusion. A total of 7689 ODX prescribing physicians were identified. Co‐location with medical oncologists who adopted the test in the early period (2008–2009) was associated with a 1.38‐fold increase in the odds of a medical oncologist adopting ODX in 2010–2011 (95% CI = 1.04–1.83), as was co‐location with early‐adopting surgeons (odds ratio [OR] = 1.25, 95% CI = 1.00–1.58). Patients whose primary medical oncologist was linked to an early‐adopting surgeon through co‐location (OR = 1.17, 95% CI = 1.04–1.32) or both patient‐sharing and co‐location (OR = 1.17, 95% CI = 1.03–1.34) were more likely to receive ODX. CONCLUSIONS: Exposure to surgeon early adopters through peer networks and co‐location was predictive of ODX uptake by medical oncologists and testing of patients. Interventions focused on the role of surgeons in molecular testing may improve the implementation of best practices in breast cancer care.