Inclusion Criteria:

Phase 1 (dose escalation)

- patients with histological proven gastrointestinal neoplasms, without standard
therapy option

- measurable or evaluable disease

- >= second-line therapy (metastasized stage) Phase 2 (efficacy)

- patients with proven colorectal neoplasms

- measurable disease, metastasized

- previous chemotherapy with 5-FU/FA ("AIO-regimen")

- age between 18 and 75 years, both male and female

- life expectancy > 3 months

- WHO-performance status <= 2

- adequate bone marrow function: hemoglobin >= 10 mg/dl, neutrophils >= 2.0 *
1000000000/l, thrombocytes >= 150 * 1000000000/l

- adequate renal and liver function: bilirubin <= 1.25 * ULN(<= 1.5 ULN * by liver
metastases), creatinine <= 1.25 * ULN, ASAT and ALAT <= 3 * ULN (<= 5* ULN by liver
metastases; AP <= 3* ULN

- written informed consent prior to inclusion into the study

Exclusion Criteria:

- pretreated with mitomycin c

- contraindication concerning 5-FU (e.g. anxiety, myocardial infarction within last 6
months, significant toxicities during previous therapy with 5-FU

- florid infections

- ileus or subileus, morbus crohn or colitis, ulcerative

- actual chronic diarrhea

- other uncontrolled severe concurrent disease excluding cytotoxic intervention

- second malignancy except basal cell carcinoma or cervical carcinoma in situ

- known cns metastases or carcinomatous leptomeningitis

- pregnancy or lactation period

- no effective contraception

- concomitant treatment with another antineoplastic agents

- participation in another clinical trial within the last 4 weeks

- patients being unwilling or unable to undergo trial specific procedures