606 Background: Genomic grade index (GGI) is a 97-gene signature which improves accuracy and prognostic value of histological grading (HG) in invasive breast carcinoma (IBC). GGI is particularly useful in segregating HG2 tumors into low or high Genomic Grade (GG1 and GG3). We aimed at prospectively evaluating the feasibility to implement GGI in routine practice with the primary objective of obtaining GGI in at least 80% of fresh tumor samples collected at surgery. Secondary objectives include GGI classification performance and impact on treatment recommendations. METHODS Eligible patients were pT1pT2 or operable pT3, N0-3 IBC. Fresh surgical samples with a H&E slide representative of the tumor specimen were sent at room temperature in the MapQuantKit for centralized analysis. Genomic profiles (Affymetrix U133 Plus 2.0) were determined for samples containing ≥ 30% invasive tumor cells and GGI calculated using the Ipsogen MapQuantDx protocol, which defines tumors as GG1 or GG3. RESULTS Between Jan and Dec 2010, 173 pts were recruited in eight centers in Belgium and 151 were eligible (21 pts N >3, 1 pt no IBC). MapQuant test was performed in 138 cases (excluding 8 tumors too small for sampling, 3 samples forgotten, 2 with no H&E slide) and GGI was obtained in 78% of cases (n=108). Reasons for failures were: 15 samples with <30% of invasive tumor cells (11%), 14 insufficient RNA quality (10%) and 1 failed hybridization (<1%). For tumors with an available representative sample (≥ 30% inv. tumor cells) (n=123) the success rate was 88%. Of 138 tumor samples collected, 77% were N0, 81% were ER+, 10% HER2+ and 9% triple negative; median tumor size was 17mm (range 6-55). The HG1, HG2 and HG3 frequencies were 24%, 48% and 28% resp. Concordance between HG1/HG3 Histologic and GG1/GG3 Genomic grading was 90%. GGI reclassified 67% of the 52 HG2 tumors as GG1 (51%) or GG3 (49%) leading to a total of 34% GG1 (n=37), 44% GG3 (n=47) and 22% undetermined (UD) (n=24). CONCLUSIONS Genomic Grade is feasible in routine clinical practice with a success rate of 88% when a representative tumor sample is provided. The impact of GGI on treatment decision will be presented at the meeting.