Malignant transformation of oral lichen planus

Abstract

The malignant transformation rate of oral lichen planus is a much debated issue. In a recent review, Mattsson et al. make an admirable effort to summarise and discuss data from two prospective and nine retrospective studies, in which ‘‘uniform and accurate information is available’’ and in which ‘‘the diagnostic criteria of oral lichen planus (OLP) have been defined’’. Based on data retrieved from these 11 papers, the authors conclude that there is an increased although low incidence of oral cancer in OLP patients. They therefore state that it is justified to regard OLP as a premalignant condition. Mainly for economic reasons, the authors further suggest that the malignant transformation rate (0.5—2% in the majority of studies) is too low to justify an extensive and costly recall program of OLP cases. These arguments are well taken by the authors. However, they also remark extensively on the diagnostic dilemma of OLP, in the sense that lichenoid contact reactions (LCR) may have been included in some previous studies, hence reported erroneously as OLP. This may have distorted the true prevalence figure of OLP. As the only example, the authors refer to a Swedish study by Axell showing an OLP prevalence figure of 1.86% but remark that at that time ‘‘LCR was not recognised as a disease entity’’, therefore casting doubts about this figure. Notably, there is an extensive microscopical overlap between OLP and LCR, even though LCR cases may exhibit a more variable histopathologic pattern than classic OLP. It may also be of some historical interest to mention, that when we suggested to our Scandinavian Oral Pathology group in the late 1970s that the histopathology of OLP was in fact ‘‘lichenoid’’, it met with much opposition. Nowadays, this is a widely recognised concept and there is a more widely accepted tendency to regard ‘‘oral lichen planus’’ (OLP) or ‘‘lichenoid contact reactions’’ (LCR) as subtypes of ’’oral lichenoid reactions’’ (e.g. Bratel et al.). Mattsson et al. conclude that their selected 11 studies ‘‘fulfilled explicitly defined diagnostic criteria’’ of OLP, indirectly suggesting that the 11 studies were also undisputable on the particular point of clearly defining and excluding cases of LCR. They further state, that LCR lesions ‘‘are not known to be associated with malignant transformation’’. We fully agree with Mattsson et al. that data are non-existent on malignant transformation of LCR. However, since inclusion or not of LCR in malignant transformation studies of OLP would seem to be a critically significant point of their review, we have somewhat at our surprise found that a majority of their 11 selected papers fail to explicitly mention or even comment upon LCR, thereby being no different from Axell’s study. Briefly, our own analysis of the 11 papers showed the following. In all the studies, OLP was diagnosed by a biopsy. Possible inclusion of LCR type lesions is suggested in only a single study but explicit mentioning of exclusion of such lesions is hard to find. In fact, there is no mentioning of LCR at all in Holmstrup and Pindborg, Silverman et al., Holmstrup et al., Salem, Silverman et al., Barnard et al. and Lo Muzio et al. In the discussion by Duffey et al., ‘‘dental amalgams’’ but not LCR was mentioned only in general terms. In the study by Rajentheran et al., their 832 cases had a histologically proven diagnosis of OLP ‘‘or lichenoid reaction’’ but no further mentioning of any possible association with dental restorations, i.e. of