Changes over time in the impact of gene‐expression profiles on the administration of adjuvant chemotherapy in estrogen receptor positive early stage breast cancer patients: A nationwide study

Ten years ago gene‐expression profiles were introduced to aid adjuvant chemotherapy decision making in breast cancer. Since then subsequent national guidelines gradually expanded the indication area for adjuvant chemotherapy. In this nation‐wide study the evolution of the proportion of patients with estrogen‐receptor positive (ER+) tumors receiving adjuvant chemotherapy in relation to gene‐expression profile use in patient groups that became newly eligible for chemotherapy according to national guideline changes over time is assessed. Data on all surgically treated early breast cancer patients diagnosed between 2004–2006 and 2012–2014 were obtained from the Netherlands Cancer Registry. ER+/Her2− patients with tumor‐characteristics making them eligible for gene‐expression testing in both cohorts and a discordant chemotherapy recommendation over time (2004 guideline not recommending and 2012 guideline recommending chemotherapy) were identified. We identified 3,864 patients eligible for gene‐expression profile use during both periods. Gene‐expression profiles were deployed in 5% and 35% of the patients in the respective periods. In both periods the majority of patients was assigned to a low genomic risk‐profile (67% and 69%, respectively) and high adherence rates to the test result were observed (86% and 91%, respectively). Without deploying a gene‐expression profile 8% and 52% (p