Prognostic value of the genomic grade index (GGi) as compared to centrally measured Ki-67 IHC and mitotic index in early breast cancer patients

Abstract

11094 Background: Genomic grading has been proposed to improve tumor grading. The genomic grade index (GGi) is a 97-gene continuous measure which resolves 80% of histological grade 2 (HG 2) tumors into HG 1 and HG 3 risk categories. GGi has higher prognostic value than HG in patients treated with and without systemic adjuvant endocrine and chemotherapy. A key issue is whether the GGi adds prognostic information to centrally-determined mitotic index and Ki-67 IHC. Methods: The control arm of the PACS 01 trial included 996 women with node-positive (N+) early breast cancer treated with six cycles of fluorouracil, epirubicin, and cyclophosphamide (FEC) and tamoxifen as required. 128 genomic profiles could be obtained from available frozen tumor samples using Affymetrix U133 Plus 2.0 gene chips through the “Carte d'Identite des Tumeurs” program of the French Ligue Nationale contre le Cancer. The Genomic Grade index (GGi) was computed using Ipsogen MapQuant Dx(R). Central Elston-Ellis grade, mitotic index (mitosis / mm2), and Ki-67 IHC (% positive cells) were available for 125 patients. The GGi and histological parameters were correlated to the 5-year metastasis status (MFS-5) by ROC analysis and to the metastasis hazard (follow-up of 6.2 ± years) by Cox regression. Results: In ER+ patients (n=93), the GGi was the only significant correlate to metastasis hazard in multivariate Cox regression with histological parameters (HR = 3.5 [1.7–7.5], p<0.001). It was the best predictor of MFS-5 (ROC AUC = 0.83, p=1E-6) when compared to histological parameters (ROC AUC = 0.71, 0.72 and 0.66 resp. p=0.003 to 0.03). In HG 2 subgroup (n=43), the GGi was the only significant predictor of MFS-5 (ROC AUC = 0.81, p=0.016). Conclusions: In our sample of N+ ER+ breast cancer patients, the GGi improved prognostication compared to centrally-measured mitotic index and Ki-67 IHC used alone and in combination. Moreover, the GGi was the only prognostic factor in histological grade 2 patients. [Table: see text]