Abstract S4-4: Independent validation of Genomic Grade in the BIG 1-98 study

Abstract

Abstract Background: We have reported that a 97-gene signature, the Genomic Grade Index (GGI) can separate histological grade (HG) 2 breast tumors into low vs high GGI tumors with different outcomes. We have also developed a quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) tool including 6 reporter and 3 control genes that can reliably evaluate Genomic Grade (GG) in paraffin embedded tumors. Methods: We evaluated the qRT-PCR GG in women treated with either tamoxifen or letrozole monotherapy in the Breast International Group (BIG) 1–98 study with 8.1 year median follow-up. The association between continuous GG and distant recurrence-free interval (DRFI) was evaluated in Cox regression models stratified for the 2 vs 4 arm randomization option, chemotherapy and hormonotherapy use, with and without adjustment for clinicopathological characteristics. Estrogen, progesterone receptor (ER, PR), Ki67 and HG were centrally reviewed. The clinicopathological model included age and log2 tumor size, ER and PR as continuous variables, nodal status (N0 vs 1–3 vs >3), HG (1 vs 2 vs 3) and HER2 (negative vs positive). Similar analyses were performed for log2 Ki67 as continuous variable. Added prognostic value was assessed using the likelihood ratio statistic. Results: We obtained GG in 883 (62%) of 1428 samples. Non evaluable results were due to pre-analytical issues or technical failure. Among the 883 patients, 521 (59%) had N0 disease, 435 (49%) were treated with tamoxifen and 84 (10%) had distant recurrences. The GG classified 502 patients with HG2 tumors as either GG1 (N = 202, 40%), equivocal (N = 220, 44%) or GG3 (N = 80, 16%). In univariate analysis, increasing GG and Ki67 were significantly associated with lower DRFI (Table). When the 773 N0/1-3 patients were analyzed based on HG, the Kaplan-Meier estimate for 10-year DRFI was 98% (95% confidence intervals 96–100%) for the 123 HG1, 92% (88–95%) for the 456 HG2 and 84% (78–90%) for the 194 HG3 patients. In the N0/1-3 population, 10 year DRFI based on GG was 95% (96–100%) for the 290 GG1, 92% (89–95%) for the 309 GG equivocal and 84% (77–90%) for the 178 GG3 patients. Interestingly, when the 456 HG2 and N0/1-3 patients were analyzed based on GG, the 10-year DRFI was 95% (92–100%) for the 185 HG2/GG1 patients, 92% (88–96%) for the 202 HG2/GG equivocal patients, 86% (76–96%) for the 69 HG2/GG3 patients. In all patients either GG or Ki67 as continuous variable significantly improved the clinicopathological model in predicting distant recurrence (Table). Conclusion: Either Genomic Grade or centrally reviewed Ki67 provides independent prognostic information for risk of distant recurrence beyond clinicopathological characteristics in patients treated with endocrine therapy. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr S4-4.