A method for the isolation and purification of a cancer recognition (CARE) antigen about 66,000 Dalton molecular weight with a pH between 4.5 and 6.5, and detection of antibodies to this CARE antigen (CARE antibody). The CARE antigen and CARE antibody are cancer markers for a broad range of cancers and can be detected in fluids or tissues of cancer patients with simple ELISA assays. The combined use of these assays for both the CARE antigen and the CARE antibody provide improved sensitivity and selectivity for cancer detection compared to assaying for the antigen or antibody alone. The CARE antigen and antibodies to this antigen have therapeutic usefulness.