Distribution of residual disease in the peritoneum following neoadjuvant chemotherapy in advanced epithelial ovarian cancer and its potential therapeutic implications.

Introduction: Residual disease in 'normal appearing' peritoneum is seen in nearly 30% of the patients following neoadjuvant chemotherapy (NACT) for advanced ovarian cancer. The goal was to study the sequence of response in different regions, the commonest sites of occult residual disease, its incidence in different peritoneal regions and the potential therapeutic implications of these.

Methods: This was a prospective multi-centre study (July 2018-June 2019). Pathological evaluation of cytoreductive surgery specimens was performed according to a fixed protocol. Prevalence of residual disease in different regions was used to study patterns of response and distribution of residual disease.

Result: In 85 patients treated between July 2018 to June 2019, microscopic disease in 'normal appearing' peritoneal regions was seen in 22 (25.2%) and in normal peritoneum around tumor nodules in 30 (35.2%) patients. Regions 4 and 8 of Sugarbaker's PCI had the highest incidence of occult disease and regions 9 and 10 the lowest. The response to chemotherapy occurred in a similar manner in over 95%- the least common site of residual disease was the small bowel mesentery, followed by upper regions (regions 1-3), omentum and middle regions (regions 0, 4, 8), lower regions (regions 5-7) and lastly the ovaries.

Conclusions: During interval CRS, based on the disease mapping provided in this manuscript, regions that have a high probability of residual disease should be explored and dissected. Complete resection of involved the peritoneal region can completely address the occult disease. The role of resection of the entire region as well as 'normal appearing' parietal peritoneal regions should be prospectively evaluated.