The prognostic and predictive impact of genomic grade index (GGI) versus central grade or molecular class in intermediate-risk breast cancer (BC): Results from the EC-Doc trial.

Abstract

1092 Background: Potential markers for adjuvant taxane-based chemotherapy (CTx) in early, intermediate-risk BC include histologic grade (HG), Ki-67, Genomic Grade (GG) or molecular classification. The randomized EC-Doc trial demonstrated improvements in DFS and OS for EC-Doc vs. FEC in patients with 1-3 positive LN. Methods: Centrally assessed protein expression data by IHC, histology/HG (n=772) and GG (n=476) were obtained. Luminal A/B classes were defined as: ER/PR+/KI-67<20/>20% and/or HER2+. Correlations/concordance of these factors were estimated; impact on DFS and value for predicting taxane-based CTx benefit was assessed. Results: Low, equivocal and high GG (GG-1/-EQ/-3) categories were observed among 54 (11%); 60 (13%); 358 patients (76%) and associated with decreasing 5-yr-DFS rates of 100%, 92% and 82% (p < 0.001).There is only 60% concordance between local (L)/central(C) HG assessments and 63% between GG and C-HG. 37.7% of GG-3 tumors were L- HG3 vs. 72% C-HG3; 79% of C-HG2 and 83% of L-HG2 tumors were re-classified (56-71% to GGI3). Only 5.6-6% of GG1 were HG1 by L/C-HG respectively.GG was prognostic only in L-HG subgroups.In univariate subgroup analyses, EC-Doc was significantly superior to FEC: C-G3 (HR=0.58, 0.39-0.93), high Ki-67 (HR=0.55, 0.32E0.92) and GG-3 (HR=0.58, 0.34-0.99) subgroups. In multivariate analyses of HR+ disease (including age, therapy, GGI category, tumor size, LN status, central/local HG, Ki-67, HER2), either C-HG3 / high Ki-67 (as dichotomous variables) or C-HG3 / GGI (as continuous variable) were identified as independent prognostic factors.In interaction analysis, only C-HG, luminal A subtype and interaction of luminal-B/therapy were significant. If local HG was included instead of C-HG, only GG was as independent prognostic factor. Conclusions: These data support GGI as independent prognostic factor in early HR+ BC and as predictive marker regarding taxane benefit by univariate analysis. There is heterogeneity between L/C-HG and GGI. C-HG and Ki-67 assessment appear similarly informative. A predictive effect regarding benefit of taxane-containing CTx was seen in the IHC-luminal B subtype.