Aims: Osteopontin (OPN) is a matricellular protein involved in tissue remodelling, cell-mediated immunity and malignant transformation. High OPN serum levels predict poor prognosis in non-small cell carcinoma and set patients with malignant pleural mesothelioma (MM) apart from disease-free asbestos-exposed individuals. Yet neither the spectrum of tissue expression nor the signalling pathways of OPN in MM and pulmonary adenocarcinoma have been characterized, although in vitro evidence links OPN to the epidermal growth factor receptor (EGFR) pathway. The aim of this study was to address these deficiencies.
Methods and results: OPN expression was investigated immunohistochemically in 104 adenocarcinomas and 38 MM and correlated with histological features, including tumour type, grade and proliferation and with expression of activated intermediary EGFR signalling pathway molecules p65, p-AKT, p-ERK, p-STAT-3, and of metalloproteinase (MMP)-1, MMP-2 and MMP-9. In MM, OPN expression was widespread (36/38) and independent of the molecular parameters studied. In adenocarcinoma, high OPN expression was correlated with expression of p65, p-ERK and MMP-9.
Conclusions: Frequent OPN expression is typical of, but not specific for MM, whereas it appears to select adenocarcinoma cases with p65 and MMP-9 expression, suggesting a link with EGFR signalling pathways.