OUTLINE: Randomized, unblinded study. Arm I: Single-Agent Chemotherapy with Drug Modulation. Fluorouracil, 5-FU, NSC-19893; with Leucovorin calcium, CF, NSC-3590. Arm II: Observation followed by Single-Agent Chemotherapy with Drug Modulation. Clinical observation until symptomatic; followed by 5-FU; with CF.