Population-based study of the effect of gene expression profiling on adjuvant chemotherapy use in breast cancer patients under the age of 65 years.

ABSTRACT

BACKGROUND: Gene expression profiling (GEP) testing can help to predict the risk of cancer recurrence and guide decisions about adjuvant chemotherapy for breast cancer (BC). However, no prior US studies have evaluated the relation between GEP testing and the use of adjuvant chemotherapy by women treated in a general oncology practice. METHODS: Eligible patients were women under the age 65 of years who were newly diagnosed with their first stage I or II, hormone receptor-positive BC between 2006 and 2011 (n = 9405). This retrospective study was conducted with a data set consisting of registry data, health claims data, and GEP testing results. The distribution of GEP test results was reported in terms of the risk of recurrence predicted, and logistic regression was used to assess the association of test results with chemotherapy use, with adjustments made for multiple patient characteristics. RESULTS: The proportions of tested women with low, intermediate, and high recurrence score results were 51%, 39%, and 10%, respectively. Among these women, 11%, 47%, and 88%, respectively, received adjuvant chemotherapy. There was a significant, positive linear relation of assay scores with chemotherapy use within the low and intermediate subgroups after adjustments for all other factors (adjusted odds ratios, 1.17 and 1.20, respectively). CONCLUSIONS: Adjuvant chemotherapy use after GEP testing is generally consistent with the recommended test interpretation for women with a high or low predicted risk of recurrence. Chemotherapy use in the intermediate-risk group increased with Recurrence Score values, and evidence from ongoing randomized trials may help to clarify whether this finding reflects optimal interpretation of GEP test results. These results demonstrate the principle that genomic testing, on the basis of research establishing its utility, can be applied appropriately in general practice in accordance with guideline recommendations.