Introduction/Background The factors affecting the rate of optimal CR for patients with advanced ovarian cancer were investigated in primary and interval cytoreductive surgery. The aim of this study to develop a scoring system that is foreseen the patients who will be able to optimal CR

Methodology We conducted a retrospective analysis of patients who were diagnosed with advanced ovarian cancer and underwent primary and interval cytoreduction at our clinic between 2010 and 2020

Results Total 340 patients that 180 and 160 of them had undergone primary and interval CR, respectively was included in this study. In primary CR group, ascites volume, presence of peritonitis carcinomatosis (PC) and para-aortic nodal metastasis (at preoperative imaging) were found the factors that effected the residual tumor volume. Presence of PC and paraaortic metastasis was detected the factors significantly effect the rate of suboptimal CR (> 1cm residual disease in this group. In interval CR group, only the ca 125 level and PC at preoperative imaging was significantly related to residual tumor volume. In contras to primary CR group, unique factor that significantly effect to optimal cytoreduction (<1 cm residual tümör) was plasma Ca 125 level. According to the logistic regression analysis performed by combining the two groups, it is found that Ca 125 level (< 500 U/ml), no PC and no paraaortic metastasis at preoperative imaging were positive factors for < 5 cm residual disease.

Conclusion According to the results of our study, preoperative variables, including serum CA 125 level, peritonitis carcinomatosis and paraaortic metastasis significantly affect the optimal cytoreduction rate in both primary and interval cytoreduction for ovarian cancer patients. A scoring system using these 3 can detect optimal ( <5 mm residual) cytoreduction group with the high rate in advanced stage ovarian cancer.

Disclosures We developed a scoring system using these 3 factors giving score 0 for patients having 3 positive factors, score 1 for patients having 2 positive factors, score 2 having 1 positive factor and score 3 no positive factor. According this scoring system, it is found that the rate of < 5 mm residual tumor volume 90%, 80%, 61% and 39% in score 0, 1,2, and 3 patients, respectively