Irinotecan Followed By Fluorouracil and Leucovorin in Treating Patients With Stage III or Stage IV Colorectal Carcinoma (Cancer), Other Refractory Carcinoma, or Metastatic Adenoma (Cancer) of Unknown Primary Origin

OBJECTIVES: * Determine the response rate in patients with stage IV colorectal carcinoma or other carcinomas treated with irinotecan followed by fluorouracil and leucovorin calcium. * Determine the disease-free survival of patients with stage III colorectal carcinoma, other refractory carcinomas, or metastatic adenocarcinomas of unknown primary site treated with this regimen. * Determine the toxicity of this regimen in these patients. OUTLINE: Patients with stage III colorectal carcinoma (post surgical resection) receive irinotecan IV over 1 hour on days 1-5 and days 8-12. Treatment repeats every 3 weeks for 2 courses. Beginning on week 7, patients receive pelvic irradiation, leucovorin calcium IV over 4 hours, and fluorouracil IV over 5-15 minutes beginning 1 hour into leucovorin calcium infusion on days 1-5. Treatment repeats every 3 weeks for a total of 2 courses. Patients with no evidence of disease may repeat the above 12-week block of chemotherapy without pelvic irradiation up to 4 times over 1 year. Patients with stage IV colorectal carcinoma, other refractory carcinomas, or metastatic adenocarcinomas of unknown primary site receive the above 12-week block of chemotherapy (irinotecan, fluorouracil, and leucovorin calcium) with pelvic irradiation (if indicated). Pelvic irradiation patients with an unresected primary tumor undergo exploratory surgery 4-5 weeks after completion of radiotherapy, even in the absence of visible tumor regression. Radical resection is attempted to effect local control and control of long term symptoms related to the primary tumor. Patients with complete response (CR) or partial response (PR) after both chemotherapy and surgery repeat the above 12-week block of chemotherapy 3 times over 1 year in the absence of disease progression or unacceptable toxicity. Patients with CR or PR after chemotherapy but no response after surgery receive irinotecan IV over 1 hour on days 1-5 and days 8-12 every 3 weeks for 1 year in the absence of disease progression or unacceptable toxicity. Patients with stable disease (SD) or progressive disease after 2 courses of irinotecan and SD, CR, or PR after surgery receive leucovorin calcium and fluorouracil as above every 3 weeks for 1 year in the absence of disease progression or unacceptable toxicity. Patients are followed every 3 months for 1 year and then every 6 months for 3 years. PROJECTED ACCRUAL: A total of 10 patients will be accrued for this study within 4 years.