Complete disease removal has the greatest impact in the treatment of advanced ovarian cancer, both during primary debulking surgery (PDS) and interval debulking surgery (IDS), but, contrarily to PDS, no consensus exist on the interpretation of the absence of residual tumor at IDS. In addition, chemotherapy induces fibrotic changes that can hinder the surgeon's ability to properly assess the spread of abdominal disease. The aim of the study is to evaluate the accuracy of visual inspection compared to histopathological examination at the level of the diaphragmatic peritoneum in patients undergoing surgery after neoadjuvant chemotherapy.

All data of patients subjected to IDS between October 2016 and October 2019 with evidence of suspected or certain residual disease at the level of the right diaphragmatic peritoneum, at intra-operative evaluation have been collected. Diaphragmatic peritoneum was classified as negative, not-surely pathologic and certainly pathologic by the surgeon, and based on the surgeon's opinion, a diaphragmatic biopsy or peritonectomy was then performed. The definition of not-surely pathologic diaphragmatic peritoneum was given in association with the presence of flat dyschromic areas, while the definition of certainly pathological diaphragmatic peritoneum was given when isolated or confluent thick nodules were visualized at the intra-operative inspection. Residual disease was indicated at the end of each intervention and classified as no residual disease (RD=0, complete cytoreduction), less than 1 centimeter (RD </= 1 cm, optimal cytoreduction) or more than 1 cm (RD > 1 cm, sub-optimal cytoreduction).

Pathological specimens' results were also divided in negative (no evidence of disease), microscopic evidence of residual disease (</= 3 mm) or macroscopic signs of residual disease (> 3 mm). Microscopic and macroscopic disease were both considered as positive for residual disease.

General early post-operative complications (arising within 30 days from surgery), and complications related to diaphragmatic peritonectomy, as post-operative pleural effusion, were classified using the extended Clavien-Dindo classification of surgical complications.

The primary end-point of the study was to evaluate the accuracy, sensitivity and specificity of the visual inspection compared to histopathological examination, at the level of the right diaphragmatic peritoneum, in patients subjected to IDS.

The secondary endpoints were to evaluate the rate of early postoperative complications related to diaphragmatic peritonectomy and assess whether this procedure may delay the re-start of post-operative chemotherapy.

Inclusion Criteria:

• patients with histology proven biopsy of epithelial ovarian, fallopian or peritoneal cancer (FIGO stage III C - IV B), judged suitable for IDS by clinicians, with evidence of suspected or certain residual disease at the level of the right diaphragmatic peritoneum, at intraoperative evaluation.

Exclusion Criteria:

• Patients with no evidence of diaphragmatic disease during IDS, and who therefore did not undergo diaphragmatic peritonectomy or biopsy

Patients with histology proven biopsy of epithelial ovarian, fallopian or peritoneal cancer (FIGO stage III C - IV B), judged suitable for IDS by clinicians, with evidence of suspected or certain residual disease at the level of the right diaphragmatic peritoneum, at intraoperative evaluation.