On the identification of biomarkers for non-small cell lung cancer in serum and pleural effusion.

The current imperative need for new biomarkers of non-small cell lung cancer (NSCLC) prompted us to compare the proteome of serum and pleural effusion samples from cancer patients with those with benign lung diseases as pneumonia or tuberculosis. Samples were prefractionated through affinity chromatography prior to 2D-DIGE to detect proteins with altered expression in cancer patients. Overall, we identified more potential biomarkers in pleural effusion, which is closer to the affected organ, than in serum. Nevertheless, in both cases principal component analysis demonstrated that the pattern of significantly altered proteins discriminates between disease groups. The biomarker candidates comprise proteins increased in malignant pleural effusions as gelsolin and the metalloproteinase inhibitor 2, and others with lower levels as S100-A8 and S100-A9. The most interesting protein was the pigment epithelium-derived factor (PEDF), which is related to angiogenesis inhibition, and was significantly overexpressed both in serum and pleural effusion from NSCLC patients. More than 12 PEDF isoforms were specifically immunodetected in both fluids in 2-D blots, most of them overexpressed in NSCLC. Thus, further validation would be ideally directed to quantify individual PEDF isoforms, as it may be only one or some of them the ones altered in the cancer process.