OBJECTIVE(S): 10-40% of advanced rectal cancer patients undergoing neoadjuvant chemoradiation achieve a pathologic complete response (pCR), which is associated with improved recurrence-free survival. This study evaluates predictors of pCR.
METHODS:Between 1997 and 2007, 342 consecutive patients with stage II and III rectal cancer who underwent neoadjuvant chemoradiation were identified from a single-institution IRB-approved colorectal cancer database. 100 patients were excluded due to concurrent IBD, FAP, HNPCC, other malignancy, urgent surgery, incomplete chemoradiation or insufficient data. Treatment was 5-FU based and the median radiotherapy dose was 5040 (4000-6100) cGy. For analysis, the cohort was stratified in 2 groups according to pathologic response (pCR/no-pCR). Pretreatment variables (see table 1) were analyzed by univariate and multivariate analysis with pCR as the dependent variable. Fischer’s exact test, Chi square, Wilcoxon rank-sum and logistic regression were used for analysis. p<0.05 was considered statistically significant.
RESULTS: A summary of the results is shown in the table. Patient demographics were statistically the same. 58 (24%) patients obtained pCR. An interval from completion of treatment to surgical resection greater than 7 weeks was significantly associated with a higher rate of pCR.
CONCLUSIONS: 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 complete pathological response.

Table1

Variable	No pCR No=184 (76.0%)	pCR No=58 (24.0%	p	Variable	No pCR No=184 (76.0%)	pCR No=58 (24.0%	p
Gender Female	46 (70.8%)	19 (29.2%)	0.41	Clinical T2	1 (16.7%)	5 (83.3%)	0.76
Gender Female	137 (77.8%)	39 (22.2%)		Clinical T3	163 (76.5%)	50 (23.5%)
Age (years)	58.5(19-86)	55.5(30-85)	0.51	Clinical T4	10 (90.9%)	1 (9.1%)
Interval ≤7weeks	71 (83.5%)	14 (16.5%)	0.021	Clinical N0	109 (74.7%)	37 (25.3%)	0.54
Interval >7weeks	63 (69.2%)	28 (30.8%)		Clinical N1	61 (78.2%)	17 (21.8%)
XRT fields 3	71 (76.3%)	22 (23.7%)	0.46	Clinical N2	5 (71.4%)	2 (28.6%)
XRT fields 4	21 (80.8%)	5 (19.2%)		Differentiation Poor	30 (88.2%)	4 (11.8%)	0.8
CEA (ng/mL)	5.17 +/- 6.46	4.04 +/- 5.52	0.3	Differentiation Moderate	123 (76.9%)	37 (23.1%)
Distance Anal Verge (cm)	5.55 +/- 2.76	5.35 +/- 2.72	0.57	Differentiation Well	24 (82.8%)	5 (17.2%)