Ex vivo evaluation of preoperatively treated rectal cancer specimens of patients undergoing radical resection

Background. Previous reports have suggested that a subset of patients with advanced rectal cancer that demonstrate minimal or no residual disease after neoadjuvant treatment may either be followed closely or may undergo local resection. We prospectively evaluated ex vivo local excision specimens of patients undergoing radical resection after preoperative chemoradiation. Methods. Patients with newly diagnosed rectal cancer received preoperative chemoradiotherapy followed by total mesorectal excision. Once removed, an ex vivo excision of the tumor bed mimicking a local excision was performed on the back table. Both the ex vivo and mesorectal specimens were inked and assessed. Results. Thirty-seven rectal cancer patients (38% stage II, 62% stage III) were prospectively enrolled onto this study. Tumor downstaging occurred in 35% and nodal status downstaging in 16% of patients. The margins around the primary tumor on all ex vivo local excision specimens were negative. Twenty-nine percent of preoperatively staged stage II cancers either remained at stage II or were upstaged to stage III (21%), while 52% of stage III tumors remained node positive at final pathologic examination. The overall complete response rate was 14%. Conclusions. A significant number of stage II cancers will have positive nodes at final pathology, and most stage III rectal cancers will remain so at final pathologic examination. Given the high percentage of patients with positive lymph nodes after chemoradiation, radical resection is still recommended for cure for stage II and III rectal cancers.