Mouse monoclonal antibody CC3C195, which detects elevated levels of its antigen in sera from many patients with colon and pancreatic cancer, binds with high affinity to the sialylated human Lea blood group antigen NeuAc alpha 2-3Gal beta 1-3 [Fuc alpha 1-4]GlcNac . . . and with lower affinity to the Lea blood group antigen itself.