Background: A pre-operative predictive biomarker of CC0 interval debulking surgery (IDS) likelihood would be helpful. The modeled CA125 elimination rate constant KELIM predicts OS in 1st line setting (You et al. Clin Cancer Res 2019). The predictive/prognostic values of KELIM regarding CC scores at IDS, and survivals, during neo-adjuvant chemotherapy were assessed. Methods: The data of the CHIVA randomized phase II trial, comparing carboplatin-paclitaxel +/- nintedanib before IDS (NCT01583322), were used. A semi-mechanistic model was built to describe CA125 longitudinal kinetics during the first 100 treatment days. The relationships between KELIM and IDS CC scores, PFS & OS, were assessed with other major prognostic factors (grade, histology, GCIG CA125 response, FIGO stage, and arm) using multivariate logistic regression (logit), C-index & survival tests. Results: The longitudinal kinetics of 529 CA125 values, assessed every 3 weeks during neo-adj chemotherapy, were modeled in 133 patients (out of 188). KELIM (as a continuous covariate) was the only significant predictive factor of CC0 IDS likelihood using multivariate analyses (OR = 12.37, 95% CI [4.32-39.67]). CC0 IDS probability can be estimated with patient KELIM: ≥ 90 % if standardized KELIM ≥ 0.12. Non-parametric survival models confirmed the independent predictive values of KELIM categorized by terciles regarding PFS & OS (Table). The parametric model linking KELIM (as a continuous covariate) with OS allows to predict the patient survivals (months) based on their estimated KELIM (HR = 0.20, [0.10-0.39]). Conclusions: The prognostic & predictive values of the modeled CA125 KELIM are also confirmed regarding CC0 IDS likelihood, PFS and OS with neo-adjuvant chemotherapy. Patient KELIM is calculable online, based on observed CA125 values, on http://www.biomarker-kinetics.org/. Clinical trial information: 2011-006288-23.