Malignant transformation to oral cancer by subtype of oral potentially malignant disorder: A prospective cohort study of Taiwanese nationwide oral cancer screening program

Objectives: To elucidate the risk of malignant transformation to invasive oral cancer by subtypes of oral potentially malignant disorders (OPMD) and to examine the independent effects of risk factors, particularly alcohol drinking, by subtype based on a nationwide oral cancer screening program targeting at general population with habits of smoking and/or betel quids chewing. Materials and methods: The total of 8501 subjects diagnosed as different subtypes of OPMDs from the Taiwanese screening program between 2004 and 2009 were followed up over time to ascertain the occurrence of invasive oral cancer. The hazard ratios of malignant transformation were estimated by using Cox proportional hazards regression model. Results: The overall malignant rate (per 1000 person-years) to oral cancer was 8.4 (407 incident cases with an average of 5.7 years of follow-up). The highest rate was noted in exophytic verrucous hyperplasia (33), followed by erythroplakia (11.8), erythroleukoplakia (10.7), oral submucous fibrosis (OSF) (8.6), and leukoplakia (5.4). After adjusting for confounders, exophytic verrucous hyperplasia still had a 5.69 (4.47–7.24) times risk compared with leukoplakia. The corresponding figures for erythroplakia, erythroleukoplakia, and OSF were 2.25 (1.31–3.89), 2.00 (1.13–3.53), and 1.63 (1.29–2.06), respectively. Alcohol drinking elevated the overall risk of malignant transformation by 23% (1–52% and also triggered a higher risk in OSF (aHR = 1.62 (1.06–2.47)). The higher risk attributed to betel quids chewing was noted for exophytic verrucous hyperplasia (aHR = 4.23 (1.55–11.55)). Conclusions: The risk of malignant transformation to oral cancer varied with the subtypes of OPMD and was elevated in OSF and verrucous hyperplasia attributed to alcohol drinking and betel quids, respectively.