Preoperative staging of irradiated rectal cancers using digital rectal examination, computed tomography, endorectal ultrasound, and magnetic resonance imaging does not accurately predict T0,N0 pathology

PURPOSE: The postradiation preoperative staging results of 25 patients with rectal cancer who were found to have Stage T0,N0 lesions after surgery were examined. Our aim was to assess the ability of preoperative staging following radiation therapy to predict the absence of disease. METHODS: From 1983 to 1994, 25 patients treated with preoperative radiation therapy for biopsy-proven rectal cancer were found to have no pathologic evidence of disease in the resected specimen (T0,N0). The preoperative postradiation disease staging results of these patients were compared with the postoperative pathologic findings. Each patient received 4,500 to 5,580 cGy during a five-week to six-week period, and four patients had preoperative chemotherapy. Surgical resection was performed six to eight weeks after completion of radiation therapy. All 25 patients were staged by digital rectal examination before surgery. In addition, 13 patients were assessed using computed tomography, 6 by endorectal ultrasound, and 1 by magnetic resonance imaging. RESULTS: Most irradiated lesions were overstaged by radiologic assessment and physical examination. No technique could reliably distinguish between postradiation fibrosis and residual cancer. The negative predictive value for digital rectal examination was 24 percent. Computed tomography accurately staged 23 percent of lesions, and endorectal ultrasound predicted 17 percent of lesions correctly. The single patient evaluated by magnetic resonance imaging was overstaged and thought to have a T2 lesion. CONCLUSIONS: Our ability to assess local eradication of rectal cancer following radiation therapy remains poor. Conventional imaging and clinical examination techniques are unable to safely predict which patients do not require surgical excision following curative radiation therapy for rectal cancer.