A prospective pathologic analysis using whole-mount sections of rectal cancer following preoperative combined modality therapy: Implications for sphincter preservation

OBJECTIVE: The aims of this study were to use a comprehensive whole-mount pathologic analysis to characterize microscopic patterns of residual disease, as well as circumferential and distal resection margins, in rectal cancer treated with preoperative CMT; and to identify clinicopathologic factors associated with residual disease. SUMMARY BACKGROUND DATA: Recent studies have shown that preoperative combined modality therapy (CMT) for rectal cancer enhances rates of sphincter preservation. However, the efficacy of preoperative CMT in conjunction with a total mesorectal excision (TME)-based resection, in terms of resection margins using whole-mount sections, has not been reported. Furthermore, since patterns of residual disease and extent of distal spread following preoperative CMT are largely unknown, intraoperative determination of distal rectal transection remains a surgical challenge. METHODS: We prospectively accrued 109 patients with endorectal ultrasound (ERUS)-staged, locally advanced rectal cancer (T2-T4 and/or N1), located a median distance of 7 cm from the anal verge, requiring preoperative CMT, and undergoing a TME-based resection. Comprehensive whole-mount pathologic analysis was performed, with particular emphasis on extent of residual disease, margin status, and intramural tumor extension. Clinicopathologic factors associated with residual disease were identified. RESULTS: A sphincter-preserving resection was feasible in 87 patients (80%), and in all 109 patients, distal margins were negative (median, 2.1 cm; range, 0.4-10 cm). Intramural extension beyond the gross mucosal edge of residual tumor was observed in only 2 patients (1.8%), both ≤0.95 cm. There were no positive circumferential margins (median, 10 mm; range, 1-28 mm), although 6 were less than or equal to 1 mm. On multivariate analysis, residual disease was observed more frequently in distally located tumors (distance from anal verge <5 cm) (P = 0.03). CONCLUSION: Our comprehensive pathologic analysis suggests that, following preoperative CMT and a TME-based resection, distal margins of 1 cm may provide for complete removal of locally advanced rectal cancer. Although residual cancer following preoperative CMT was more likely in the setting of distally located tumors, occult tumor beneath the mucosal edge was rare and, when present, limited to less than 1 cm. Our results extend the indications for sphincter preservation, as distal resection margins of only 1 cm may be acceptable for rectal cancer treated with preoperative CMT.