Prospective study on Oncotype DX® assay to assess recurrence risk in early ER-positive HER2-negative breast cancer patients with uncertain biological behavior by standard parameters and its impact on treatment recommendation: The POST trial.

Background: Data published in 2015 showed that patients with early breast cancer (EBC) and a low-risk (LR) Recurrence Score® (RS) result by the 21-gene Oncotype DX® assay ("the test") did not derive benefit from adding chemotherapy (CT) to endocrine therapy (HT), while those with a high-risk (HR) RS result did. However, the role of CT remained uncertain in patients with intermediate-risk (IR) cancers. We designed a study to assess the test's ability to categorize patients with EBC with uncertain biological behavior into the groups (LR and HR) for which the value of additional chemotherapy was defined.

Methods: The POST trial was a multicenter, prospective cohort study conducted in 14 Breast Centers of the Tuscany region of Italy. Consecutive patients with pT1-2 pN0-N1mi hormone receptor-positive/HER2-negative EBC and uncertain biological behavior based on standard parameters were enrolled. Patients were categorized based on RS results into LR, IR, and HR groups if RS result was < 11, 11-25, and > 25, respectively. Treatment recommendations by multidisciplinary meeting assessed before and after RS results were available.

Results: Of 246 tested samples, 78 were classified as LR or HR, with most of the patients (65.4 %) being at IR. Following test results, the recommendation changed in 15.9 % of cases. Among patients initially recommended for CT or for discussion about the role of CT, respectively 64.3 % and 75.9 % ultimately received recommendation for HT alone.

Conclusions: Our study suggests that RS results can refine treatment decisions for patients with EBC exhibiting uncertain biological behavior initially recommended or considered for CT. (250/250).