134P Impact of pre-operative MammaPrint/BluePrint use for final treatment decisions in patients with stage II/IIIa HR+/HER2- early-stage breast cancer eligible for neoadjuvant chemotherapy: The DETERMIND study

MammaPrint (MP) and BluePrint (BP) signatures have been validated in the adjuvant setting to identify patients for which chemotherapy (CT) could be spare. Neoadjuvant Chemotherapy (NCT) is a common approach (pts) with clinically high-risk Early Breast Cancer (EBC). Other options include neoadjuvant endocrine therapy (NET) or primary surgery particularly those low-risk luminal tumors. In DETERMIND study, we explore whether pre-operative use of MP/BP may help clinicians reinforce best treatment strategy patients. prospective, open-label, multicenter assessing utility signature on decision-making process optimal operable HR+/HER2- EBC, stage II-IIIA (up N1) recommendation NCT. A total 165 pts included 11 centers. Patient data will collected at inclusion (baseline), time results 1- 3-years follow-up. This initial analysis includes first 99 pts: Median age was 57 years (range 31-85), 94% were II, 51% cN1. By MP/BP, 37 (37%) classified as Luminal A, 58 (59%) Luminal-B, 4 cases presented non-Luminal phenotype (3 Basal, 1 HER2). line results, 44 did not receive group, 35 (95%) NCT, 19 it replaced by NET. Patients MP High-Risk received NCT 53 (85%). The confidence final decision physicians significantly increased result. clinical EBC criteria there high prevalence (35%) who able de-escalate also further supported administered majority (85%) High Risk. Our findings support risk guide provide information shared-decision making.