Patterns of pathological response to neoadjuvant chemotherapy and its clinical implications in patients undergoing interval cytoreductive surgery for advanced serous epithelial ovarian cancer- A study by the Indian Network for Development of Peritoneal Surface Oncology (INDEPSO).

Objectives: The goals were to study • The pattern of pathological response to neoadjuvant chemotherapy (NACT) and its clinical implications • The impact of chemotherapy response grade (CRG) on survival METHODS: A retrospective analysis of patients undergoing interval cytoreductive surgery (CRS) between January 2013 to December 2017 was performed. The surgical and pathological reports were analyzed and surgical and pathological PCI compared. The pathological response to chemotherapy was assessed using the score developed by Bohm. et al.

Results: In 79 patients, it was observed that sites involved by disease first like ovaries and pelvic peritoneum (lower region) were the last to respond preceded by the omentum, right upper quadrant (RUQ) peritoneum (upper region) and parietal peritoneum (middle region). Microscopic residual disease was seen in 20.2% in normal looking areas of peritoneum and in 20% with no gross residual disease in the RUQ. Visual inspection during surgery overestimated the disease extent in 40.5% and underestimated it in 15.1%. There was no difference in the progression free (p = 0.587) and overall survival (p = 0.157) between patients with CRG 1, 2 and 3 (poor, moderate, and complete/near complete response, respectively). Retroperitoneal nodes were positive in 0% with CRG 3, 27.5% with CRG 2 and 72.7% with CRG 1 (p < 0.0001).

Conclusions: The pathological response to NACT follows a specific pattern. Visual inspection is of limited value in assessing disease extent following NACT. Surgery following NACT should target sites involved before NACT and not just residual disease. The response in regional nodes should be included in chemotherapy response scores.