A tumor-associated core-region carbohydrate antigen of epithelial mucin, expressed in most colon carcinoma, mucinous carcinoma, pancreatic cancer, gastric, lung, breast, and ovarian carcinoma. Sialosyl-Tn (STn) antigen has been shown to be highly sensitive and a specific marker of colorectal cancer, associated with more aggressive diseases and poor prognosis. STn antigen and its immediate precursor, Tn antigen, are mucin type glycoprotein structures associated with the earliest steps of mucin O-linked glycosylation. When combined with a carrier molecule, keyhole limpet hemocyanin (KLH), this antigen may be co-administered with oral cyclophosphamide as an immune modulator.