553 Background: The prognostic value of LI of CC has been demonstrated by several groups. However no validated test is available for clinical practice. We previously described an automated and reproducible method for testing LI (Allard MA et al 2012) and aimed to validate it for clinical use. Methods: According to NIH criteria, we designed a prospective analysis of this biomarker in pts included in the PETACC8 phase III study. Primary objective was to compare % of pts without recurrence at 2 years in pts with high versus low LI (#NCT02364024). Secondary objectives were comparison of disease free (DFS) and overall (OS) survivals, and prognostic value of LI on these endpoints. Automated testing of LI was performed on virtual slides without access to clinical data. Results: Among the 1,220 CC pts enrolled, LI was high, low and not evaluable in 241 (20%), 790 (65%) and 189 (15%), respectively. High and low LI groups did not differ except for treatment arm (p=0.04) and microsatellite status (MSI/MSS) status (p...