Publication: ESMO Breast, Presentation ID: 65P

Authors: Elena Shagisultanova, V. Borges, R. Layeequr Rahman, E. Brown, L. Gold, L. Matt-Amaral, L. Samiian, C.Godellas, B.A. Lesnikoski, G. Srkalovic, A. Shah, C. Collins, T. Bah, S. Uygun, N. Stivers, A. Menicucci, W. Audeh, J. A. O’Shaughnessy

Title: Prognostic Performance of MammaPrint in Patients with Small T1a, b, and c Node-Negative Early Breast Cancer

Abstract

Background:
The incidence of small, node-negative (T1a,b,c N0) early breast cancer (EBC) is increasing in mammography-screened populations. Although outcomes are generally favorable, biologic heterogeneity complicates treatment decision-making. Genomic assays such as MammaPrint® (MP) enable biologically informed risk stratification. We evaluated the prognostic performance of MP in patients (pts) with T1N0 EBC.

Methods:
This analysis included 4,349 pts with T1N0 EBC enrolled in the prospective FLEX Study who received MP and BluePrint® (BP) testing with 3.2 years median follow-up data. Tumor sizes were 414 T1a, 1,551 T1b, and 2,384 T1c. Clinical subtypes were 87% HR+HER2–, 5% HER2+, and 4% TNBC. Recurrence-free survival (RFS) was evaluated using Kaplan–Meier (KM) and multivariable Cox proportional hazards models for all pts and the HR+HER2– subgroup.

Results:
The median age was 63, 82% of pts were post-menopausal, and 14% had grade 3 cancer. Among all tumors, 10% were MP High Risk 2 (H2), 31% High Risk 1 (H1), 40% Low Risk (LR), and 19% were UltraLow (UL) Risk (p<0.001), while for BP there were 7% Basal, 2% HER2, 32% Luminal B, and 59% Luminal A (p<0.001). Among the HR+HER2- subgroup, 5% had H2, 30% H1, 43% LR, 21% UL (p<0.001), and for BP 3% had Basal, 0.1% HER2, 32% Luminal B, and 65% Luminal A (p<0.001). KM and multivariable analysis showed MP H2 was associated with significantly worse RFS among all pts and the HR+HER2- subgroup (Table).

Conclusion:
Among this cohort of pts with clinically early-stage (T1N0 EBC), MP identified pts with H2 tumors (10% overall and 5% among pts with HR+HER2– disease) who experienced significantly worse outcomes compared with those with H1 and LR/UL cancers. These findings highlight the prognostic value of MP in clinically small EBC and indicate that a subset of pts with T1N0 may benefit from escalated therapy and biology-informed treatment approaches.