At a workshop coordinated by the WHO Collaborating Centre for Oral Cancer and Pre-cancer in the UK issues related to potentially malignant disorders of the oral cavity were discussed by an expert group. The consensus views of the Working Group are presented in a series of papers. In this report we review the literature on the epidemiology and natural history of potentially malignant disorders (PMD), detailing those characteristics of the patients and lesions thought to be associated with future development of oral squamous cell carcinoma (OSCC). Older patients, particularly females are more at risk than younger patients; the duration of PMD may be important. Those who have never used tobacco seem at greater risk than smokers. OSCC is more likely with PMD on the lateral and ventral tongue, floor of mouth and retromolar/soft palate complex than with those elsewhere. The vast majority of PMD in which OSCC develop are non-homogenous although 5% of homogenous PMD will develop carcinoma. Large lesions covering several intraoral subsites also appear more at risk.

Grading of selected features in OSCC is reliable and can facilitate treatment planning.

This retrospective laboratory-based study investigates the potential for malignant transformation of oral mucosal lesions in a population of 1.6 million. Over the 20-year period there were 745 patients diagnosed with primary intra-oral squamous cell carcinoma (OSCC), 165 patients with dysplasia and 1182 patients with 'non-dysplastic' lesions (epithelial hyperplasia, hyperkeratosis epithelial atrophy, lichen planus and lupus erythematosus). Malignant transformation occurred in 15% of dysplasias and in 1% of 'non-dysplastic' lesions at average intervals after diagnosis of 48 and 65 months respectively. Only 6% of patients with OSCC had a pre-invasive lesion biopsied. These data suggest that white lesions are only rarely the pre-invasive phase of OSCC. It is possible therefore that early changes are red, small or even microscopic with carcinoma developing without a clinically observable phase. More effective management strategies will require the development of tissue markers to enhance early detection.

This study confirms and extends previous findings that suprabasal p53 immunoexpression has a high PPV for malignant transformation of PMOLs and can be used as a specific marker for lesions that are at high risk for malignant transformation. The absence of suprabasal p53 staining (that is, absence of, or basal, p53 staining) is non-informative for prognostic purposes. Because of its limited sensitivity, p53 IHC is not a substitute for the assessment of dysplasia in the evaluation of PMOLs. Instead, p53 IHC emerges as a clinically useful supplement of histopathological assessment in the prognosis of PMOLs.

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