A vaccine containing a pancarcinoma carbohydrate antigen conjugated with keyhole limpet hemocyanin (KLH), with potential antineoplastic activity. Sialylated Tn antigen (sTn) is a monosaccharide glycan usually O-linked to serine or threonine residues of mucins found on most epithelial cancers. Conjugation with KLH, a hapten carrier and an immunostimulant, improves host immune responses. Vaccination with sTn-KLH vaccine may produce antibodies and elicit a cytotoxic T lymphocyte (CTL) response against those tumor cells expressing sTn, resulting in decreased tumor growth.