Potentially malignant oral lesions in northern Ireland: a 20-year population-based perspective of malignant transformation.

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.