Clinical assessment following preoperative combined modality therapy (CMT) for rectal carcinoma does not accurately predict pathologic response: A prospective analysis

Abstract

3536 Background: Accurate preoperative assessment of rectal carcinoma response to neoadjuvant CMT may guide subsequent therapy, including extent of resection. Our aim was to determine the accuracy of this clinical assessment in a prospective manner. Methods: The study group consisted of 94 prospectively accrued patients with locally advanced (bulky or endorectal ultrasound T3/T4 and/or N1) rectal carcinoma at a median distance of 6.75 cm from the anal verge (range 0–13 cm) treated with preoperative CMT (5040 cGy with 5-FU-based chemotherapy) followed by radical surgery with total mesorectal excision. The operating surgeon prospectively assessed the tumor in terms of specific parameters: mobility, morphology, and circumference of lesion prior to initiation of CMT. Under anesthesia, the same operating surgeon estimated tumor response based upon the same specific parameters and categorized the extent of response into 5 groups: 1=progression; 2= 0–29%; 3=30–59%; 4=60–89%; and 5=greater than 90% response. Percent pathologic tumor response was determined prospectively using whole mount sections and categorized into the same groups. Results: Clinical estimate of tumor response was correct in 21 (22.3%) cases and underestimated pathologic response in 73 (77.7%) cases. There were no clinical overestimates of response. The specificity of clinical exam in determining complete or near-complete pathologic response (≥95% tumor regression) was 68.5%, the sensitivity was 19%, the positive predictive value was 14.8%, the negative predictive value was 74.6%, and the accuracy was 57.4%. Distance from anal verge (p=0.6) and preoperative tumor stage (p=0.94) had no significant impact on clinical estimation of tumor response. Conclusions: Clinical examination underestimates extent of rectal carcinoma response to preoperative CMT in over 75% of patients. Given the importance of preoperative CMT and interest in sphincter preservation, our results emphasize the need to develop accurate methods for determining rectal cancer response to CMT. No significant financial relationships to disclose.