Background: PARP inhibitors (PARPi) are approved therapies in high grade serous ovarian cancer (HGSOC). There are few studies after PARPi progression and correlation with dynamic changes in resistance. We hypothesized that PARPi resistance could be overcome by adding an anti-angiogenic. Methods: We report the first phase 2 trial assessing the combination of olaparib and cediranib after PARPi failure in HGSOC. This investigator initiated study included three cohorts of 10 evaluable patients (pts): i) platinum sensitive post PARPi (PS), ii) platinum resistant post PARPi (PR) and iii) exploratory cohort of pts re-challenged with chemotherapy post PARPi progression (PE) (NCT02681237). The primary objective was to determine objective response rate by RECIST v1.1 and progression free survival (PFS) at 16 weeks. Secondary objectives were to evaluate safety, PFS, overall survival (OS) and mechanisms of PARPi resistance. Pts who had radiographic progression on any PARPi were eligible. Archival tumor at initial diagnosis and baseline tumor biopsy at PARPi progression were mandatory. Pts received olaparib tablets 150mg BID with cediranib 20mg QD until progression or unacceptable toxicity. CT scans were performed every 8 weeks. Whole exome and RNA sequencing were performed on paired tumors tissues. Results: Thirty-four pts were enrolled. BRCA1/2 mutations were found in 9/11 PS, 8/10 PR and 7/13 PE pts. By RECIST1.1, four partial responses were observed (2 in PR and 2 in PE cohorts) and 18 stable disease. The 16−week PFS was 54.5% (31.8−93.6) in PS, 50% (26.9−92.9) in PR and 36% (15.6−82.8) in PE, respectively. OS at 1 year was 81.8% (61.9−100) in PS, 64.8% (39.3−100) in PR and 39.1% (14.7−100) in PE. Main related adverse events were anemia, hypertension, diarrhea and fatigue, grade 3 < 10%. Molecular analyses identified different mechanisms of PARPi resistance in ~77% of evaluable pts with matched pre-post PARPi progression biopsies such as reversion mutations in BRCA1/2 and other homologous repair (HR) genes; BRCA, HR and MDR upregulation, CCNE amplification and RIG-I like receptor downregulation. Conclusions: Treatment with olaparib-cediranib after PARPi failure was feasible and met the predefined bar for efficacy in each cohort. This is the largest clinical trial prospectively evaluating PARPi failure and correlating tissue genomic mechanisms of resistance. Clinical trial information: NCT02681237