Objective The objective of the study was to evaluate the prognostic impact of residual tumor size after cytoreductive surgery in patients with epithelial ovarian cancer.

Methods In this prospective, multicenter study, 226 patients with epithelial ovarian cancer (International Federation of Gynecology and Obstetrics stages IIA–IV) were included. Patients were treated with cytoreductive surgery and adjuvant platinum-based chemotherapy. Univariate and multivariable survival analyses were performed to investigate the impact of residual tumor size on progression-free and overall survival.

Results In 69.4% of patients, surgery resulted in complete tumor resection; minimal residual disease (≤1 cm) was achieved in 87.2% of patients. Advanced tumor stage was associated with a lower rate of complete tumor resection (P < 0.001). After cytoreductive surgery, 3-year overall survival rates were 72.4%, 65.8%, and 45.2% for patients without, with minimal, and with gross residual disease (>1 cm), respectively (P < 0.001). Multivariable survival analysis revealed residual tumor size (P = 0.04) and older patient age (P = 0.02) as independent prognosticators for impaired overall survival. Complete cytoreduction was predictive for a higher rate of treatment response (P = 0.001) and was associated with prolonged progression-free and overall survival (P < 0.001 and P = 0.001).

Conclusions The size of residual disease after cytoreduction is one of the most crucial prognostic factors for patients with ovarian cancer. Patients after complete cytoreduction have a superior outcome compared with patients with residual disease. Leaving no residual tumor has to be the aim of primary surgery for ovarian cancer; therefore, patients should receive treatment at centers able to undertake complex cytoreductive procedures.