Background: Circulating tumor cells (CTC) are detected in 12–30% of advanced stage/relapsing ovarian carcinoma (OC). We evaluated the prognostic value of CTC counts among patients (pts) from the ANTHALYA trial, an open-label randomized phase II study evaluating addition of bevacizumab (Beva) to neoadjuvant carboplatin-paclitaxel (CP) in first line for pts with unresectable FIGO stage IIIc/IV ovarian, tubal or peritoneal adenocarcinoma. Methods: We obtained CTC counts at baseline and before interval debulking surgery (IDS). A CTC threshold of ≥ 1 CTC/7.5 mL blood was considered as CTC+. We assessed the prognostic impact of CTCs on objective response rate (ORR), interval debulking surgery (IDS) rate, complete resection rate and progression-free survival (PFS), and explored their potential predictive impact on ORR and PFS according to bevacizumab therapy. Results: In 88 pts with an available CTC count at baseline, CTC+ pts (n = 29) had a 75.9% ORR (at IDS), vs 59.3% for pts with 0 CTC (n = 59): OR = 2.2 [0.8-5.8] (OR-adj=1.8 [0.8-5.8]). Respectively, 58.6% vs 66.1% were amenable to IDS and 55.2% vs 54.2% achieved a complete resection. Median PFS was 21 m [15.0-25.4] in CTC+ pts and 25.8 m [18.5-27.2] in pts with 0 CTC (HR = 1.5 [0.8-2.8] and HR-adj=1.7 [0.9-3.2]). CTC counts at IDS were available in 70 pts. At IDS, a complete resection was achieved in 66.7% of CTC+ pts (n = 6), and in 68.8% of pts with 0 CTC (n = 64). Exploration of the potential predictive impact of CTC is described in the table.Table947PPrognostic approach0 CTC at baseline (n = 59)CTC+ at baseline (n = 29)ORR at IDS59.3%75.9%Median PFS [95% CI]25.8 m [18.5-27.2]21.0 m [15.0-25.4]Predictive approachBeva (n = 36)CP (n = 23)Beva (n = 17)CP (n = 12)ORR at IDS61.1%56.5%82.4%66.7%Median PFS [95% CI]25.8 [20.9-NE]20.3 [13.8-27.2]21.0 [15.0-30.6]20.6 [8.0-25.4]Progression rate at M3636.1%56.5%52.9%83.3% Open table in a new tab Conclusions: Baseline CTC counts in OC patients receiving neoadjuvant chemotherapy +/- bevacizumab carry dual prognostic information: CTC count at IDS do not add any information, CTC+ seems to be associated with a higher ORR, while 0 CTC count seems to be a prognostic factor with better PFS, in the whole population and among patients treated with bevacizumab. Clinical trial identification: 2012-01144-22 Legal entity responsible for the study: ROCHE Funding: Roche Disclosure: T. de La Motte Rouge: Consultancy work: AstraZeneca, Roche, MSD, Eisai, Sanofi Travel grants/meeting support: Roche, Novartis, Pfizer Corporate-sponsored research: Novartis. P. Cottu: Novartis, Roche, AstraZeneca, Nanostring, Pfizer. P. Pautier: Membership on an advisory board or board of directors: Roche: Travel grants/meeting support: Roche, Astra Zeneca, Pharmamar Corporate-sponsored research; Pharmamar, Novartis. A. Floquet: Membership on an advisory board or board of directors: Roche, AstraZeneca; Travel grants/meeting support: Roche, AstraZeneca. F. Selle: Consultancy work: Roche: Travel grants/meeting support: Roche, AstraZeneca, Pharmamar. M. Fabbro: Travel grants/meeting support: Roche. E. Kalbacher: Travel grants/meeting support: Roche, Pharmamar, GSK, Leo Pharma, AstraZeneca. P. Follana: Consultancy work: AstraZeneca, Novartis Travel grants/meeting support: Roche, AstraZeneca, Amgen. A.F. Lesoin: Employment: Centre Oscar Lambret, Lille. J. Medioni: Membership on an advisory board or board of directors: AstraZeneca, Pierre Fabre Consultancy work: Clovis Oncology; Travel grants/meeting support: Roche, Sanofi Aventis. J. Dupin: Employment: Roche. R-M. Ferri: Employment: Roche SAS. C. Dubot: Corporate-sponsored research: Roche. R. Rouzier: Membership on an advisory board or board of directors: Roche; Consultancy work: Roche; Travel grants/meeting support: Roche; Corporate-sponsored research: Roche. F. Joly Lobbedez: Consultancy work: AstraZeneca, Janssen, Tesaro, Roche, Sanofi, Novartis, Bristol-Myers Squib Travel grants/meeting support: Roche, Janssen, AstraZeneca, Tesaro Corporate-sponsored research: Astellas, Janssen. All other authors have declared no conflicts of interest.