OBJECTIVE: This study evaluates factors associated with a pathologic complete response (pCR) after neoadjuvant chemoradiation for rectal cancer.

SUMMARY BACKGROUND DATA: Approximately 20% of rectal cancer patients undergoing neoadjuvant chemoradiation achieve pCR, which has been associated with decreased local recurrence and improved recurrence-free survival. Means of predicting pCR remain incompletely defined.

METHODS: A total of 306 consecutive patients with stage II or stage III rectal cancer who underwent neoadjuvant chemoradiation then surgery between 1997 and 2007 were identified from a single-institution. Sixty-four patients with concurrent inflammatory bowel disease, hereditary colorectal cancer, other malignancy, urgent surgery, incomplete chemoradiation, or insufficient data were excluded. All patients received neoadjuvant 5-FU-based chemotherapy and external beam radiation. Histologic response was categorized as pCR or not-pCR, which defined the 2 study cohorts. Variables were analyzed by univariate and multivariate analysis with pCR as the dependent variable. Fisher exact test, chi2, Wilcoxon rank-sum, and logistic regression were used for analysis. P< 0.05 was considered statistically significant.

RESULTS: Of the total patients, 242 were studied, including 58 (24%) that achieved pCR. The 2 groups were statistically similar in terms of age, gender, body mass index, tumor differentiation, radiation dose, and pretreatment stage. On multivariate analysis, an interval ≥ 8 weeks between treatment completion and surgical resection was significantly associated with a higher rate of pCR, which correlated with decreased local recurrence and improved overall survival.

CONCLUSION: Despite traditional beliefs that certain patient and tumor factors influence pCR, an extended interval between completion of neoadjuvant therapy and surgery was the single most important determinant in achieving a pCR.