Patients receive irinotecan IV over 30 minutes followed 7 hours later by flavopiridol IV over 1 hour on days 1, 8, 15, and 22. Treatment continues every 6 weeks for a minimum of 2 courses in the absence of disease progression or unacceptable toxicity. During the first week of the second course, patients receive flavopiridol alone on day 1 and irinotecan alone on day 2.