Plasminogen activation system in oral cancer: Relevance in prognosis and therapy (Review)

Research on carcinogenesis and progress in cancer treatment have reduced mortality of cancer patients. Mortality rates decreased by 1.5% per year from 2001 through 2010 for most types of cancer in men and women. However, oral cancer is still a significant global health problem since incidence and mortality rates are increasing. Oral cavity cancer is ranked the 8th in men and the 14th in women based on data collected between 2006 and 2010 by the National Institute of Health. Furthermore, an increasing incidence of head and neck neoplasms, particularly the tongue cancer among young adults has been reported recently. It is most likely due to increasing human papillomavirus (HPV) infection or the early start of tobacco and alcohol consumption. Treatment of oral cancer patients is mainly surgical and often leads to esthetic and functional deformities, with severe impact on the quality of life. Thus, novel form of treatments and selection of patients with high and low risk of mortality is of high priority for clinical studies. The expression of proteolytic enzymes in tumor and stromal tissues has been shown to have prognostic significance in many human cancers and inhibiting proteolysis can reduce tumor growth in many in vivo and in vitro models. Plasmin, with its activators and inhibitors are of great importance in many human malignances and collectively are called plasminogen activation system (PAS). In this comprehensive review we examine expression, possible prognostic markers and importance for therapy of the PAS members in oral cancer. Literature review suggests that overexpression of urokinase and its receptor are markers of poor outcome, thus, their inhibition can be explored in oral cancer therapy. Role of plasminogen activator inhibitor (PAI-1) is complex and depends on its concentration. Overexpression of PAI-1 favors angiogenesis, metastasis and poor prognosis, although when applied in very high concentrations it inhibits angiogenesis and tumor growth, the phenomenon is described as the PAI-1 paradox.