Gastric cancers (GCs) are often diagnosed in advanced stages, owing to non-specific clinical symptoms at early stages that resemble Acid Peptic Diseases (APDs). Despite recent efforts, a simple, liquid biopsy-based, multi-protein panel pre-diagnostic assay that can differentiate GCs from APDs is lacking. Parallelly, Mass Spectrometry (MS)-based targeted proteomics methods including Multiple Reaction Monitoring (MRM) are being progressively utilised as method-of-choice to build Laboratory Developed Tests (LDTs). An MS-MRM LDT that can quantify a panel of serum proteins was developed and tested in 135 serum samples from treatment-naïve cases of GCs, APDs, and healthy individuals.