Recently, it was demonstrated that an increased level of NeuNAc alpha2-3Gal beta1-4(Fuc alpha1-3)GlcNAc beta-R (sialyl Le(x)) and NeuNAc alpha2-3Gal beta1-3(Fuc alpha1-4)GlcNAc beta-R (sialyl Le(a)) expression on the surface of colorectal cancer cells is positively correlated with progression of the disease. It has not been determined, however, which type of glycans, N- or O-glycans, is more closely associated with progression when cancer cells express those oligosaccharides. To address this problem, we have examined expression of sialyl Le(a) and sialyl Le(x), those oligosaccharides in O-glycans, and core 2 beta-1,6-N-acetylglucosaminyltransferase (C2GnT) transcripts in colorectal cancer specimens from 46 patients and compared those results with clinicopathological variables. C2GnT is a glycosyltransferase that is responsible for the core 2 branch, which is critical for biosynthesis of sialyl Le(a) and sialyl Le(x) in O-glycans. Sialyl Le(a) and sialyl Le(x) were determined by immunohistochemistry, and C2GnT transcripts were detected by reverse transcription-PCR. Sialyl Le(a) or sialyl Le(x) in O-glycans was assessed by combining immunohistochemistry for sialyl Le(a) or sialyl Le(x) with reverse transcription-PCR for C2GnT. Sialyl Le(a), detected on cancer cells in 74% of patients, was well correlated with lymph node metastasis, whereas sialyl Le(a) and sialyl Le(x) in O-glycans, which were specifically detected in cancer tissues of 50 and 61% of patients, respectively, were closely associated with lymphatic and venous invasion. In addition, C2GnT, which was specifically detected in cancer tissues of 63% of patients, was closely correlated with the vessel invasion, as well as depth of tumor invasion. These results strongly suggest that sialyl Le(a) and sialyl Le(x) in O-glycans and C2GnT, expressed in cancer cells, may play important roles in tumor progression through vessel or direct invasion.