Clinical and Radiologic Predictors of a Pathologic Complete Response to Neoadjuvant Chemotherapy (NACT) in Patients Undergoing Cytoreductive Surgery for Colorectal Peritoneal Metastases: Results of a Prospective Multi-center Study.

backgroundPatients undergoing cytoreductive surgery for colorectal peritoneal metastases who have a pathologic complete response (pCR) to neoadjuvant chemotherapy experience a significantly longer survival than those with residual disease. This response is known only after surgery. This study aimed to examine clinical and radiologic predictors of a pCR.

methodsFrom July 2018 to December 2019, the study prospectively enrolled 120 patients. The clinical and radiologic findings were compared between patients with and without a pCR. A protocol for pathologic evaluation was followed.

resultsA pCR was observed in 34 patients (28.3%). Receiver operating characteristic (ROC) curves showed that patients with a surgical Peritoneal Cancer Index (sPCI) of 3 or lower had an 80% probability of experiencing a pCR, and that patients with a radiologic PCI (rPCI) of 2 or lower had a 70% probability of experiencing a pCR. A pCR was correctly predicted for 47% of the patients by imaging and for 44.4% of the patients by surgical evaluation. The site of primary tumor, the timing of peritoneal metastasis (PM), histology, tumor marker positivity, and mutations in known poor prognostic genes (KRAS) did not differ between the patients with and those without pCR. The primary tumor showed residual disease in 23.5% and regional nodes in 26.4% of the patients with pCR.

conclusionsThe rPCI and sPCI concurred with a pCR in less than 50% of the patients. The patients with a lower PCI had greater concordance. An sPCI of 3 or lower was predictive of a pCR in 80% of the patients. The impact of KRAS mutations on pCR should be evaluated in a larger series. The predictors of pCR and response to systemic chemotherapy should be incorporated in prognostic scores used to select patients for surgery.