Clinical examination following preoperative chemoradiation for rectal cancer is not a reliable surrogate end point

Purpose: Clinical assessment of rectal cancer response to preoperative combined-modality therapy (CMT) using digital rectal examination (DRE) has been proposed as a means of assessing efficacy of therapy. However, because the accuracy of this approach has not been established, we conducted a prospective analysis to determine the operating surgeon's ability to assess response using DRE. Patients and Methods: Ninety-four prospectively accrued patients with locally advanced rectal cancer (T3/4 or N1) were evaluated with DRE and sigmoidoscopy in order to determine the following tumor characteristics: size, location, mobility, morphology, and circumference. Following preoperative CMT (50.40 Gy with fluorouracil-based chemotherapy) and under general anesthesia, the same surgeon estimated tumor response based on changes in these tumor characteristics, assessed via DRE. Percent pathologic tumor response was determined prospectively by a single pathologist using whole mount sections of the resected cancer. Results: Clinical assessment using DRE underestimated pathologic response in 73 cases (78%). In addition, DRE was able to identify only 3 of 14 cases (21%) with a pathologic complete response. There were no clinical overestimates of response. None of the clinicopathologic tumor characteristics examined had a significant impact on DRE estimation of response. Conclusion: Clinical examination underestimates the extent of rectal cancer response to preoperative CMT. Given the inaccuracy of DRE following preoperative CMT, it should not be used as a sole means of assessing efficacy of therapy nor for selecting patients following CMT for local surgical therapies.