A vaccine consisting of the oligosaccharide antigen sialyl Lewisª (CA19-9) conjugated to the nonspecific immunomodulator keyhole limpet hemocyanin (KLH), with potential antineoplastic activity. Upon administration, sialyl Lewisª-keyhole limpet hemocyanin conjugate vaccine may induce production of IgG and IgM antibodies as well as trigger an antibody-dependent cell-mediated cytotoxicity (ADCC) against tumor cells expressing the sialyl Lewisª antigen. Sialyl Lewisª is a blood group antigen and a tumor-associated antigen associated with epithelial cancers such as breast cancer and various digestive cancers. Sialyl Lewisª serves as a ligand for the cytokine-inducible cell adhesion molecule (CAM) E-selectin, an endothelial cell-specific type I transmembrane surface protein, thus facilitating hematogenous metastasis by mediating the adhesion of circulating cancer cells to vascular endothelium.