The current disclosure provides for specific peptides from the Epidermal Growth Factor Receptor (EGFR) protein and the derived ionization characteristics of those peptides that are advantageous for quantifying the EGFR directly in formalin fixed biological samples by the method of Selected Reaction Monitoring (SRM) mass spectrometry. Such fixed biological samples include: formalin-fixed tissue/cells, formalin-fixed/paraffin embedded (FFPE) tissue/cells, FFPE tissue blocks and cells from those blocks, and formalin fixed and paraffin embedded tissue culture cells. EGFR protein is quantitated in biological samples by the method of SRM/MRM mass spectrometry by quantitating one or more of the peptides described herein. The peptides can be quantitated if they reside in a modified or an unmodified form. Examples of potentially modified forms of an EGFR peptides include those bearing phosphorylation of a tyrosine, threonine, serine, and/or other amino acid residues within the peptide sequence.
