Abstract P6-13-04: IMPACt Trial: MammaPrint and BluePrint Molecular Subtyping Guide Treatment Decisions in Breast Cancer

Abstract Background: IMPACt is a prospective, case-only study to measure the effect of MammaPrint (MP) and BluePrint (BP) on treatment decisions in breast cancer patients. Here, we report the results of the primary objective in women aged ≥18 years with histologically proven invasive stage I-II, hormone receptor (HR) positive, and HER2-negative breast cancer. Methods: The study included 369 women from 18 US institutions. The recommended treatment plan was captured before and after receiving results for MP and BP. Treatment was started after obtaining results. In addition to the effect of results on physician treatment decisions involving chemotherapy (CT) and physician confidence, the distribution of MP High Risk (HR) and Low Risk (LR) patients was also evaluated. Results: MP classified patients to 62% (n=228) LR and 38% (n=141) HR. Treatment decisions were changed for 25% (n=92) of women after receiving MP and BP results. Of the LR patients initially prescribed CT, 68% (45/66) had CT removed from their treatment recommendation. Of the HR patients who initially were not prescribed CT, 66% (42/64) had CT added. Overall, 89% (202/228) of LR patients did not receive CT, and likewise 84% (119/141) of HR patients did receive CT after receiving MP. Among those who did not change treatment (n=277), 68% of physicians reported having greater confidence in their prescribed therapy. Conclusions: The IMPACt trial shows MP generates a 25% overall treatment change in clinical practice. The highest impact is for women with LR results, where 68% are spared chemotherapy in favor of endocrine therapy alone. Additionally, 73% of physicians report having higher confidence in treatment decisions for their patient after MP. Table 1: Treatment changesTreatment Decision Pre- to Post-MPMP HRMP LRTotalCT to CT772198no CT tp CT42547CT to no CT04545no CT to no CT22157179Total141228369 Citation Format: Soliman H, Rehmus E, Shah V, Srkalovic G, Mahtani R, Levine E, Mavromatis B, Srinivasiah J, Kassar M, Gabordi R, Yoder E, Qamar R, Audeh W, IMPACt Investigators Group I. IMPACt trial: MammaPrint and BluePrint molecular subtyping guide treatment decisions in breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P6-13-04.