BACKGROUND: Overexpression of fatty acid synthase (FAS), the cytosolic enzyme responsible for the conversion of dietary carbohydrates to fatty acids, has been reported in several human malignancies and pointed as a potential prognostic marker for some tumors. This study investigated whether FAS immunohistochemical expression is correlated with the clinicopathological characteristics of oral squamous cell carcinoma (OSCC). MATERIALS AND METHODS: The clinical features of 102 patients with OSCC of the tongue treated in a single institution were obtained from the medical records and all histopathological diagnoses were reviewed. The expression of FAS was determined by the standard immunoperoxidase technique in formalin-fixed and paraffin-embedded specimens and correlated with the clinicopathological characteristics of the tumors. RESULTS: Eighty-one cases (79.41%) were positive for FAS. Microscopic characteristics such as histological grade (P < 0.05), lymphatic permeation (P < 0.001), perineural infiltration (P < 0.05), and nodal metastasis (P < 0.02) were associated with FAS status. A significantly lower survival probability for patients with advanced clinical stage (log-rank test, P < 0.001), lymph nodes metastasis (log-rank test, P < 0.001), presence of vascular permeation (log-rank test, P = 0.05), and perineural invasion (log-rank test, P = 0.01) was observed in the studied samples. CONCLUSION: The expression of FAS in OSCC of the tongue is associated with the microscopic characteristics that determine disease progression and prognosis.144376382