The identification of molecules that can reliably detect the presence of a tumor or predict its behavior is one of the biggest challenges of research in cancer biology. Biological fluids are intriguing mediums, containing many molecules that express the individual health status and, accordingly, may be useful in establishing the potential risk of cancer, defining differential diagnosis and prognosis, predicting the response to treatment, and monitoring the disease progression. The existence of circulating soluble growth factor receptors (sGFRs) deriving from their membrane counterparts has stimulated the interest of researchers to investigate the use of such molecules as potential cancer biomarkers. But what are the origins of circulating sGFRs? Are they naturally occurring molecules or tumor-derived products? Among these, the epidermal growth factor receptor (EGFR) is a cell-surface molecule significantly involved in cancer development and progression; it can be processed into biological active soluble isoforms (sEGFR). We have carried out an extensive review of the currently available literature on the sEGFRs and their mechanisms of regulation and biological function, with the intent to clarify the role of these molecules in cancer (and other pathological conditions) and, on the basis of the retrieved evidences, speculate about their potential use in the clinical setting.

Assessment of biological diagnostic factors providing clinically-relevant information to guide physician decision-making are still needed for diseases with poor outcomes, such as non-small cell lung cancer (NSCLC). Epidermal growth factor receptor (EGFR) is a promising molecule in the clinical management of NSCLC. While the EGFR transmembrane form has been extensively investigated in large clinical trials, the soluble, circulating EGFR isoform (sEGFR), which may have a potential clinical use, has rarely been considered. This study investigates the use of sEGFR as a potential diagnostic biomarker for NSCLC and also characterizes the biological function of sEGFR to clarify the molecular mechanisms involved in the course of action of this protein. Plasma sEGFR levels from a heterogeneous cohort of 37 non-advanced NSCLC patients and 54 healthy subjects were analyzed by using an enzyme-linked immunosorbent assay. The biological function of sEGFR was analyzed in vitro using NSCLC cell lines, investigating effects on cell proliferation and migration. We found that plasma sEGFR was significantly decreased in the NSCLC patient group as compared to the control group (median value: 48.6 vs. 55.6 ng/mL respectively; p = 0.0002). Moreover, we demonstrated that sEGFR inhibits growth and migration of NSCLC cells in vitro through molecular mechanisms that included perturbation of EGF/EGFR cell signaling and holoreceptor internalization. These data show that sEGFR is a potential circulating biomarker with a physiological protective role, providing a first approach to the functional role of the soluble isoform of EGFR. However, the impact of these data on daily clinical practice needs to be further investigated in larger prospective studies.

Surgery in Small-Cell Lung Cancer: Past, Present and Future | InTechOpen, Published on: 2012-03-02. Authors: Cristian Rapicetta, Sara Tenconi, Tommaso Ricchetti, et