Gastric cancer (GC) or stomach cancer is the fourth most common cancer in the world  and the second leading cause of cancer related death for both genders. The onset of gastric cancer is typically without symptoms, and most stomach cancers are not diagnosed until the later stages. In accordance the survival rates are low . Diagnostic medical techniques, such as those involving an endoscopy, are invasive, expensive and generally only performed when the cancer is at an advanced stage. The ability to use a simple blood test for early detection would therefore offer a non-invasive, low cost alternative that would significantly increase the survival outcomes for those suffering from this disease.
Previous work in our group identified potential protein biomarkers for the disease, including afamin, clusterin and vitamin D binding protein , where their levels in serum were significantly reduced in comparison to healthy or benign patients.
Here we present the results of a larger cohort analysis, developed for serum, using multiple reaction monitoring (MRM) on a triple quadrupole mass spectrometer, coupled to a high performance liquid chromatograph. The study involved serum digestion and subsequent determination of protein levels using three unique peptides per protein. The optimisation process investigated levels of in source and in sample deamidation, where the in source deamidation of the target peptides was found to be the most significant.