Patients receive 1 of 3 preoperative chemoradiotherapy treatment regimens, determined by the treating physician. Within 21-56 days after the completion of chemoradiotherapy, patients undergo surgical resection. Patients receive irinotecan IV over 90 minutes and leucovorin calcium IV over 2 hours followed immediately by fluorourcil IV bolus on day 1. Treatment continues in the absence of disease progression or unacceptable toxicity.