A method of screening a biomarker for diagnosing or detecting cancer comprising steps of: providing a biological sample comprising glycosylated proteins having a N-linked glycosylation motif, which is an asparagine-linked glycosylation motif; de-glycosylating the proteins at the asparagine-linked glycosylation motif; fragmenting the de-glycosylated proteins to obtain de-glycosylated peptides comprising the asparagine-linked motif and non-glycosylated peptides comprising a non-glycosylated motif and which do not comprise the asparagine-linked motif; determining in the fragmented proteins an amount of the de-glycosylated peptide, an amount of the non-glycosylated peptide, and a ratio of the amount of the de-glycosylated peptide to the non-glycosylated peptide; and selecting the proteins as a biomarker if the ratio is changed compared to that of a control, wherein the biological sample is from a patient and the control sample is from a healthy subject, wherein the asparagine-linked glycosylation motif and the non-glycosylated peptide sequence that does not contain the asparagine-linked motif are specific for a given glycosylated protein, wherein the non-glycosylated motif for a given protein is an amino acid sequence, which is not glycosylated and is from the same protein as the protein comprising the asparagine-linked glycosylation motif and does not contain a peptide motif Asp-Xxx-Ser/Thr, cysteine and methionine residues, wherein the asparagine-linked glycosylation motif is represented by an amino acid sequence of AsnXxxSer (SEQ ID NO:3), AsnXxxThr (SEQ ID NO:4) or AsnXxxCys (SEQ ID NO:5), wherein a residue of the de-glycosylation at the motif is Asn and a peptide fragment comprising AspXxxSer (SEQ ID NO:6), AspXxxThr (SEQ ID NO:7) or AspXxxCys (SEQ ID NO:8) is generated by the de-glycosylation, wherein Xxx refers to any amino acid except proline, wherein the de-glycosylation is performed by using a PNGase-F, and wherein the amount is determined using a Mass spectrometry. providing a biological sample comprising glycosylated proteins having a N-linked glycosylation motif, which is an asparagine-linked glycosylation motif; de-glycosylating the proteins at the asparagine-linked glycosylation motif; fragmenting the de-glycosylated proteins to obtain de-glycosylated peptides comprising the asparagine-linked motif and non-glycosylated peptides comprising a non-glycosylated motif and which do not comprise the asparagine-linked motif; determining in the fragmented proteins an amount of the de-glycosylated peptide, an amount of the non-glycosylated peptide, and a ratio of the amount of the de-glycosylated peptide to the non-glycosylated peptide; and selecting the proteins as a biomarker if the ratio is changed compared to that of a control, wherein the biological sample is from a patient and the control sample is from a healthy subject, wherein the asparagine-linked glycosylation motif and the non-glycosylated peptide sequence that does not contain the asparagine-linked motif are specific for a given glycosylated protein, wherein the non-glycosylated motif for a given protein is an amino acid sequence, which is not glycosylated and is from the same protein as the protein comprising the asparagine-linked glycosylation motif and does not contain a peptide motif Asp-Xxx-Ser/Thr, cysteine and methionine residues, wherein the asparagine-linked glycosylation motif is represented by an amino acid sequence of AsnXxxSer (SEQ ID NO:3), AsnXxxThr (SEQ ID NO:4) or AsnXxxCys (SEQ ID NO:5), wherein a residue of the de-glycosylation at the motif is Asn and a peptide fragment comprising AspXxxSer (SEQ ID NO:6), AspXxxThr (SEQ ID NO:7) or AspXxxCys (SEQ ID NO:8) is generated by the de-glycosylation, wherein Xxx refers to any amino acid except proline, wherein the de-glycosylation is performed by using a PNGase-F, and wherein the amount is determined using a Mass spectrometry.