Critical increment of Lewis blood group antigen in serum by cancer found by photothermal immunoassay.
Lewis blood group antigen levels in human sera were assayed with a highly sensitive photothermal immunoassay which is based on laser-induced photothermal detection. Comparison of 32 colon cancer patients' sera and 34 healthy persons' sera showed that cancer patients' sera contained more Lewis antigens than healthy persons' sera. Le(a) antigen level in Le(a-) type persons and Le(b) level in Le(b-) type persons differentiated healthy persons and colon cancer patients. Furthermore, it was found that in Lewis blood phenotype (a-) several cancer patients' sera specimens changed to (a+). Many reports demonstrated that Lewis phenotype of erythrocytes changed with various conditions, including carcinomas, but they dealt mostly with erythrocytes and salivas or showed immunohistochemical evidence, and there are no reports on the quantitative analysis of ordinary (noncancerated) Lewis antigen levels in human sera. This is because Lewis antigens in sera, unlike those found in saliva, are too small to quantify with conventional immunoassay and there has been no highly selective method to measure Lewis antigens in sera. The increase of Lewis antigen in cancer patients' sera is presumed to antecede the blood type change. Our assay presented here, a highly sensitive assay of Lewis antigens, will greatly contribute to an early detection or diagnosis of cancers.