Cancer metastasis is an ectopic growth of malignant cells. In human colorectal cancer, it is hypothesized that, during the progression of the disease to an advanced stage, highly malignant and metastatic tumor cells arise within primary tumors and become predominant. Based on this hypothesis, molecules associated with metastatic cells have been sought by the comparison of surgical specimens from patients at various clinical stages. Colorectal carcinomas with increased metastatic potential and with poor prognosis have been characterized by a loss of an organ-specific mucin determinant (sulfomucin), by an increased expression of non-intestinal sialomucins, and by an ectopic expression of adhesion ligands (sialyl-dimeric Lex antigens) on mucins.