Pretreatment identification of patients likely to have pathologic complete response after neoadjuvant chemoradiotherapy for rectal cancer.

Purpose: In selected patients, a wait-and-see strategy after chemoradiotherapy for rectal cancer might be feasible provided that the probability of pathologic complete response (pCR) is high. This study aimed to identify clinical parameters associated with pCR. Furthermore, we attempted to identify subgroups with increased probability of pCR that might aid in clinical decision making.

Methods: A total of 6444 patients that underwent surgical resection of a single primary carcinoma of the rectum after neoadjuvant chemoradiotherapy (nCRT) between January 2009 and December 2016 in the Netherlands were included in the study. Data on the outcome variable, pCR, and potential covariates were retrieved from a nationwide database. The variables included in the analysis were selected based on previous studies and were analyzed using univariate and multivariate logistic regression analyses.

Results: pCR was observed in 1010 patients (15.7%). Pretreatment clinical tumor stage and signs of obstruction were independently associated with pCR. Nodal stage and presence of metastatic disease decreased chances of pCR significantly. The best response rate was observed in patients diagnosed with a non-obstructive, well-/moderately differentiated adenocarcinoma of the lower rectum with no clinical apparent nodal or distant metastatic disease (pCR ratio 18.8%). The percentage of patients demonstrating pCR decreased in case of symptoms of pretreatment obstruction or poorly differentiated tumors (pCR ratio of 11.8 and 6.7%, respectively).

Conclusion: This nationwide study confirms several of the previously reported clinical predictors of pCR.