Clinical Criteria Underestimate Complete Pathological Response in Rectal Cancer Treated With Neoadjuvant Chemoradiotherapy

BACKGROUND: Published criteria define specific mucosal features of clinical complete response for rectal cancer after neoadjuvant chemoradiotherapy. OBJECTIVE: The aim of this study was to determine the performance of these criteria to identify a pathological complete response. DESIGN: Histopathology reports were retrieved for consecutive rectal cancers treated with neoadjuvant therapy followed by proctectomy. The mucosal appearance of residual disease was compared with the final pathological stage. SETTING: This study was conducted at a single-institution, tertiary referral center. PATIENTS: The study included 238 patients. INTERVENTIONS: All patients underwent neoadjuvant chemoradiation followed by proctectomy between 1997 and 2007. MAIN OUTCOME MEASURES: Gross mucosal appearance was compared with the final pathological stage. RESULTS: Following neoadjuvant chemoradiation, 61 of 238 (25%) patients were downstaged to ypT0. Forty-five of these 61 patients (74%) had a residual mucosal abnormality that precluded assignment of a complete response. Of these, 40 had residual ulcers (up to 10 mm in depth) and 5 had exophytic lesions. The remaining 16 patients with pathological complete response fulfilled criteria for clinical complete response and had either no visible abnormality or a scar. Although mucosal complete clinical response was statistically associated with ypT0 status (p < 0.0001), 6 of 22 (27%) patients with mucosal complete clinical response still had residual disease. Smaller size of residual mucosal abnormality was also associated with ypT0 status (p = 0.002). LIMITATIONS: This is a retrospective study and preoperative clinical assessment of response is not recorded for comparison to resected specimens. CONCLUSIONS: The majority of patients attaining ypT0 status do not display mucosal features of complete response. When present, a mucosal complete response is statistically associated with ypT0 status, but is poorly sensitive. If rectal conservation after chemoradiation is to be pursued, alternative means of restaging are required to maximize the number who might benefit from this approach.