Patients with far advanced colorectal cancers received chemotherapy consisting of low-dose cyclophosphamide (LDCY) 333 mg/m2 every four weeks intravenously and by oral administration of 5'-DFUR (a masked compound of 5-Fluorouracil). Serum levels of immunosuppressive acidic protein (IAP), an acute phase protein, were measured every four weeks for a total of thirty-one LDCY trials of ten patients. LDCY chemotherapy significantly decreased the IAP levels in cancer patients with high IAP levels. These results suggested that LDCY chemotherapy could counteract host responses against tumors and could have decreased immunosuppressive responses in cancer patients.