Abstract
The prognosis of malignant neuroendocrine tumors of the lung is known to be very poor. Aiming to identify new markers of pulmonary neuroendocrine tumors in early stages and also differential diagnostic markers between large cell neuroendocrine carcinoma and small cell lung cancer, we comprehensively analyzed peptides which were secreted into conditioned medium by LCN1, a large cell neuroendocrine carcinoma cell line. Specific peaks in conditioned medium but not in used medium alone were detected using matrix-associated laser desorption/ionization time of flight mass spectrometry. Two peptide fragments of 40 and 19 amino acid residues were identified by matrix-associated laser desorption/ionization time of flight mass spectrometry. These two fragments were demonstrated to be parts of VGF nerve growth factor inducible (VGF), which is usually expressed in nerve cells or neuroendocrine cells. RT-PCR analysis of lung cancer cell lines showed that VGF mRNA was expressed only in neuroendocrine carcinoma–derived cells. Our data suggest that VGF can be used as a novel serological diagnostic marker of pulmonary neuroendocrine tumors.