Impact of gene-expression profiling in patients with early breast cancer when applied outside the guideline directed indication area.

PURPOSE: In Dutch guidelines, gene expression profiles (GEP) are indicated in estrogen receptor positive early breast cancer patients in whom benefit of chemotherapy (CT) is uncertain based on traditional prognostic factors alone. Aim of the present study is to assess the use and impact of GEP on administration of adjuvant CT in breast cancer patients who have according to national guidelines a clear indication to either use or withhold adjuvant chemotherapy (clinical high or low risk).

METHODS: Clinical low- and high-risk patients, according to Dutch breast cancer guidelines, diagnosed between 2011 and 2014 were selected from the Netherlands Cancer Registry. Influence of GEP use and GEP test result on CT administration was assessed with logistic regression.

RESULTS: Overall, 26,425 patients were identified; 4.8% of patients with clinical low risk (444/9354), 7.5% of the patients with a clinical high risk (1281/17,071) received a GEP. GEP use was associated with significantly increased odds of CT administration in clinical low-risk patients (OR = 2.12 95% CI: 1.44-3.11). In clinical high-risk patients, GEP use was associated with a decreased frequency of CT administration (OR = 0.55, 95% CI: 0.48-0.63). Adherence to the GEP result was higher in clinical high-risk patients with a discordant GEP result as compared to clinical low-risk patients with a discordant GEP result: 71.7% vs. 52.2%, respectively.

CONCLUSION: GEP is frequently used outside the indicated area and significantly influenced the administration of adjuvant CT, although adherence to the test result was limited.