DISEASE CHARACTERISTICS: Histologically confirmed unresectable, advanced and/or metastatic disease: Colorectal cancer Measurable or evaluable disease Epidemiologically proven fibroblast activation protein positive Failed or refused conventional treatment, and unlikely to derive significant benefit from conventional treatments No active CNS metastases No new or progressive lesions on CT scan, more than 3 months since treatment (i.e., surgery or radiotherapy) for brain metastases, and/or not receiving mitomycin Hormone receptor status: Not specified