Peptides from the tyrosine-protein kinase receptor UFO protein (AXL) are provided that are particularly advantageous for quantifying the AXL protein directly in biological samples that have been fixed in formalin by the method of Selected Reaction Monitoring (SRM)/Multiple Reaction Monitoring (MRM) mass spectrometry. Such biological samples are chemically preserved and fixed and include formalin-fixed tissue/cells, formalin-fixed/paraffin embedded (FFPE) tissue/cells, FFPE tissue blocks and cells from those blocks. A protein digest is prepared from the biological sample and the AXL protein is quantitated in the Liquid Tissue sample by the method of SRM/MRM mass spectrometry by quantitating in the protein sample at least one or more of the peptides described.