Recent studies estimated that 15 to 20% of all cancers in humans are associated with viruses. Among oral cancer about 90% are oral squamous cell carcinomas (OSCC). Alcohol and tobacco consumption have been recognized for years as the main risk factors for development of OSCCs. However, 10 to 20% of patients suffering from OSCCs are non-smokers and/ or non-drinkers. Consequently, the hypothesis of another agent responsible has risen. Indeed, several studies have suggested the possibility that a virus could be associated with or be a causal agent of OSCC. The first objective is to detect and characterize the presence of infectious agent (mostly virus) transcripts in pre-malignant or malignant tumours from patients with OSCCs.The secondary objectives are (i) to associate and (ii) if possible define a causality link between these agents and a subset of potentially malignant disorders and/or OSCCs.

Inclusion Criteria:

• Patient over 18 years,
• For subgroup "potentially malignant disorder : clinical diagnosis of leukoplakia,
• For subgroup "OSCC" : histological diagnosis of OSCC,
• Patient who never smoked, or light smoker, (≤5 pack-year) or 15 years of cessation,
• Patient who never drank, or light drinker (≤ 20 g/day for men and 10g/day for women) or 15 years of cessation,
• Informed consent signed.

Exclusion Criteria:

• Previous treatment of oral cancer,