Abstract. 4F2hc (CD98) has been associated with tumor growth, and is highly expressed in various tumors. The aim of this study was to evaluate the clinicopathological significance of 4F2hc expression in pulmonary neuroendocrine (NE) tumors. Surgically-resected patient tumors including 16 large cell neuroendocrine carcinoma (LCNEC), 12 small cell lung cancer (SCLC), 1 atypical carcinoid (AC) and 5 typical carcinoid (TC) samples were included in this study. Tumor sections were immunohistochemically stained for 4F2hc (CD98), glucose transporter 1 (Glut1) and 3 (Glut3), hypoxia-inducible factor-1α (HIF-1α), hexokinase I, vascular endothelial growth factor (VEGF), microvessel density (CD34), epidermal growth factor receptor (EGFR), Akt/mammalian target of rapamycin (mTOR) signaling pathway (p-Akt, p-mTOR and p-S6K) and for a cell cycle regulator (p53). 4F2hc was overexpressed in 0% of the pulmonary carcinoids (TCs and ACs), 62.5% of the LCNECs and 50.0% of the SCLCs. A positive 4F2hc expression was significantly associated with age, histology and Glut1 expression. Moreover, a significant correlation was found between 4F2hc expression, and Glut1, HIF-1α, p-Akt, p-mTOR and p-S6K. The expression of 4F2hc was also significantly associated with poor overall survival. The expression of 4F2hc expression tended to increase from low-grade to high-grade pulmonary NE tumors. Our results suggest that 4F2hc may play a significant role in tumor progression, hypoxic conditions and poor outcome in patients with pulmonary NE tumors.
IntroductionNeuroendocrine (NE) tumors of the lung arise from Kulchitzky cells, which are normally present in the bronchial mucosa and share the common morphological features of neuroendocrine tumors, including organoid nesting, palisading, rosettes, or a trabecular growth pattern. These tumors are represented by a wide range of pathological entities (1-5). It is now widely recognized that NE tumors of the lung include a spectrum that ranges from low-grade typical carcinoid (TC) and intermediate-grade atypical carcinoid (AC) to high-grade large cell neuroendocrine carcinoma (LCNEC) and small cell lung carcinomas (SCLC) (1-4). However, there has been no established clinical marker, which correlates with the response to the treatment and the prognosis in patients with pulmonary NE tumors. 4F2hc (CD98) is a disulphide-linked 125-kDa heterodimeric membrane glycoprotein, which is found on the cell surface of most normal cells. It was first identified on the cell surface of T lymphocytes (5). However, 4F2hc has been shown to be involved in the cellular proliferation, transformation, fusion, and adhesion and also in the L-type amino acid transport (LAT) system, in addition to regulating integrin activation, and therefore, integrin signaling and anchorage-independent growth. 4F2hc is reconstituted and expressed at high levels on the surface of many types of tumor cells. The overexpression of 4F2hc has been shown to result in cellular transformation (6,7). Recent studies have documented that 4F2hc expression is in...