Background: Quisinostat is an orally bioavailable potent pan-histone deacetylase inhibitor. Combinations of HDAC inhibitors with paclitaxel or cisplatin demonstrate promising results in preclinical models with cisplatin and paclitaxel resistant OC. In phase Ib study the dosage of Quisinostat in combination of paclitaxel and carboplatin recommended for the phase II study was 12 mg. We report results of the phase II study of Quisinostat in combination with paclitaxel and carboplatin in pts with recurrent platinum resistantOC. Methods: the main inclusion criteria was tumor progression observed not less than 1 month and no more than 6 months after completion of the planned number of cycles of 1^st line platinum/paclitaxel based CT. Quisinostat was administered at dose 12 mg p.o. each 3 week cycle on Days 1, 3, 5, 7, 9, 11 with of paclitaxel (175 mg/m²) and carboplatin (AUC5) on Day 7 of each cycle, for 2^ndline. Pts received up to 6 cycles. The primary efficacy endpoint is the objective response rate (ORR) verified by the ICR. The secondary endpoints include safety, progression free survival (PFS) and overall survival. The study design implies the use of the two-stage Simon model: 29 patients who underwent treatment would provide 80% power for hypothesis testing in order to frequency of the ORR 30% (α = 0.05). Results: 31 pts were enrolled (30 pts evaluated). Median age was 57 years. Twenty one pts (67.7%) received all 6 cycles of therapy. ORR was 50.0% (15 pts). Median duration of response was 5 months (4.2-5.7). Median PFS - 6 months (95%CI 4.4-7.6). Any SAE were seen in 16.1% pts, AE of grade 3 and 4 – in 71% and 48.4% pts temporarily discontinued therapy due to AE. Dose reduction of CT due to AE was performed in 22.6% pts. The most common adverse events were neutropenia – 67,7%, nausea – 61.3%, weakness – 29%, thrombocytopenia – 22.6%, neuropathy – 19.4%, vomiting – 19.4%. Conclusions: Quisinostat in combination with paclitaxel and carboplatin in pts with recurrent platinum resistant ovarian cancer showed high efficacy and good tolerability Clinical trial information: NCT02948075