An enzyme having an activity of transferring N-acetylglucosamine to the non-reducing end of a Gal.beta.1-4Glc or Gal.beta.1-4GlcNAc-group via a .beta.-1,3 bond; a nucleic acid encoding the same; and a method of diagnosing cancer and/or tumor, in particular, digestive cancer and/or tumor using the expression dose of a gene of the above enzyme as an indication. A gene of a novel enzyme having an activity of transferring N-acetylglucosamine to the non-reducing end of a Gal .beta.1-4Glc or Gal .beta.1-4GlcNAc-group via a .beta.-1,3 bond is cloned from human stomach cells and its base sequence is determined. Then this enzyme is expressed. Since this enzyme is scarcely or never produced in cancer and/or tumor, in particular, digestive cancer and/or tumor cells, cancer and/or tumor can be diagnosed with the use of the expression of the enzyme gene as an indication.