VTN and gastric cancer: The study employed a label-free approach of MS to quantify differentially expressed proteins in gastric cancer, and through multiple reaction monitoring analysis, four proteins—Clusterin isoform 1 (CLU-1), thrombospondin 1 (TSP1), tyrosine-protein kinase SRMS, and Vitronectin (VTN) —were identified as serum biomarkers capable of differentiating gastric cancer patients from the normal population with significant specificity and selectivity [99].