Inclusion Criteria:

- Histologic and/or cytologic diagnosis of metastatic or relapsed colorectal cancer at
any time during disease but not candidates for surgical resection.

- Prior treatment with at least 1 conventional approved therapeutic regimen.

- Subjects who have failed prior cytotoxic chemotherapy regimens containing irinotecan
(CPT-11), 5 fluorouracil (5-FU), and/or oxaliplatin for advanced (relapsed)
metastatic colon cancer are eligible

Exclusion Criteria:

- Other chemotherapy, radiotherapy, immunotherapy, or investigational agents within 4
weeks before signing the ICF (6 weeks if the previous chemotherapy included
nitrosoureas or mitomycin)

- Prior radiotherapy to >25% of bone marrow

- Prior exposure to MAC-321