The present invention describes oligosaccharide sequences, which are specifically expressed by human tumors. The present invention is related to a method of determining an oligosaccharide sequence, which comprises a tumor specific terminal N-acetylglucosamine residue, in a biological sample, the presence of said sequence in said sample being an indication of the presence of cancer. The present invention provides antigenic substances comprising said oligosaccharide sequences in a polyvalent form and it further provides diagnostic agents, pharmaceutical compositions and cancer vaccines comprising said oligosaccharide sequences or substances binding to said oligosaccharide sequences. The present invention is also related to methods for the treatment of cancer.