Objective The Chemotherapy Response Scoring (CRS) system was developed to enable reproducible reporting of histologic tumor response in interval debulking specimens following neoadjuvant chemotherapy in advanced stage tubo-ovarian high-grade serous carcinoma. This prognostic biomarker has been included in ovarian cancer pathology reporting guidelines (International Collaboration on Cancer Reporting, College of American Pathologists) and in the upcoming European Society for Medical Oncology-European Society of Gynaecological Oncology (ESMO-ESGO) guidelines for ovarian cancer management. We present follow-up data on the CRS validation initiatives and suggest research with novel therapeutic agents incorporating this biomarker.

Methods The cohort on whom CRS was originally developed was analyzed after an extended follow-up of an additional 36 months. The CRS histopathologic scoring system was applied to omental sections obtained at interval surgery from all 80 patients. Progression-free and overall survival were re-calculated.

Results After a median follow-up of 4.3 years the CRS score predicted progression-free survival with an HR of 0.39 (95% CI 0.21 to 0.70), p = 0.002 adjusted for age, stage, and debulking status (median 1.08 vs 2.27 years for CRS1/2 vs CRS3). CRS was also predictive of overall survival with an HR of 0.17 (95% CI 0.07 to 0.44), p = 0.0002 adjusted for age, stage, and debulking status (median 2.55 vs 5.47 years for CRS1/2 vs CRS3).

Conclusion CRS3 is a reproducible prognostic biomarker for improved progression-free and overall survival in stage 3C or 4 tubo-ovarian high-grade serous carcinoma after neoadjuvant chemotherapy. The score, obtained at interval debulking surgery, can help facilitate research and biomarker driven first-line treatment of patients with advanced ovarian cancer.