ARM B (closed to accrual as of 6/1/2005--currently enrolled patients may cross over to arm I for remainder of therapy): Patients receive irinotecan hydrochloride IV over 2 hours on day 1 and leucovorin calcium and fluorouracil as in arm A. Treatment repeats every 14 days for up to 12 courses in the absence of unacceptable toxicity or recurrent disease.