A method of analyzing diagnostic information, the method including: measuring a concentration of a mucin-1 (Tn-MUC1), which is reactive with a lectin that recognizes and binds to an N-acetyl-D-galactosamine→serine (threonine) residue, in a blood sample originated from a subject to be diagnosed; comparing the measured value with a threshold value; and estimating that a disease affecting the subject to be diagnosed is not prostate cancer but a benign prostate disease when the measured value of the concentration of Tn-MUC1 is greater than the threshold value.