Malignant transformation in 1458 patients with potentially malignant oral mucosal disorders: a follow-up study based in a Taiwanese hospital

BACKGROUND: It is generally accepted that the development of cancer in the oral mucosa is preceded by an identifiable non-invasive precursor lesion. The aim of this follow-up study was to estimate the rate and the time to transformation in a group of patients from southern Taiwan with potentially malignant oral epithelial lesions. METHODS: The follow-up time is defined as the duration between the onset of the initial diagnosis and the occurrence of confirmed oral cancer. A total of 1458 patients with histological diagnoses of various premalignant oral lesions were followed up between 1991 and 2001. The average age at initial diagnosis was 47.5 years. The histological diagnoses were divided into six categories: epithelial dysplasia with hyperkeratosis/epithelial hyperplasia (8.85%); epithelial dysplasia with submucous fibrosis (2.54%); submucous fibrosis (27.57%); hyperkeratosis/epithelial hyperplasia (29.01%); lichen planus (9.80%) and verrucous hyperplasia (22.22%). RESULTS: Within the cohort of 1458 patients, 44 patients progressed to oral cancer in the same site as the initial lesions with an overall transformation rate of 3.02% and a mean follow-up time of 42.64 months. Eight of the 166 patients with dysplastic lesions and 15 of 423 patients with hyperkeratosis/epithelial hyperplasia progressed to malignancy. The other patients with malignant transformation originated from various pre-cancerous oral lesions and conditions (submucous fibrosis, eight of 402; lichen planus, three of 143; verrucous hyperplasia, 10 of 324). CONCLUSION: These results indicate that patients with pre-malignant oral lesions need long-term follow up.