Thomsen-Friedenreich antigen (TF-Ag) is the disaccharide (Gal beta1-3 GalNAc alpha), which is also known as the core 1 structure. The presence of this disaccharide on the surface of approximately 90 percent of carcinomas is due to altered glycosylation in these tumors. TF-Ag plays a role in the adhesive properties of tumor cells involved in metastasis. Treatment of mice with JAA-F11, a monoclonal antibody to TF-Ag alpha inhibited lung metastasis and improved prognosis in a mouse breast cancer model. The presence of naturally occurring antibodies to TF-Ag in cancer patients is related to improved prognosis. The pancarcinoma expression of TF-Ag, combined with the evidence of a mechanistic role for TF-Ag in cancer spread, show that this target would have clinical utility. The presence of naturally occurring antibody to TF-Ag indicates that increasing the anti-TF-Ag antibody would be safe for the cancer patient and indicates that tolerance would not have to be broken to create this immune response. Finally, the prognostic improvements seen clinically and in animal models indicate that this is an important vaccine target.