Serum proteins, such as carcino-embryonic antigen, cytokeratin 19 fragment, cancer antigen 125, squamous-cell carcinoma antigen, neuron-specific enolase, progastrin-releasing peptide, tumour M2-pyruvate kinase, and C-reactive protein are potential markers for lung cancer, and their levels can signify the presence of tumours, facilitate histological analysis, and allow prediction of cancer progression. This evidence concerns the gene KRT19 and cancer.