High frequency of allelic loss in dysplastic lichenoid lesions.

Oral lichen planus (OLP) is a common mucosal condition that is considered premalignant by some, whereas others argue that only lichenoid lesions with epithelial dysplasia are at risk of progressing into oral carcinoma. A recent study from this laboratory used microsatellite analysis to evaluate OLP for loss of heterozygosity (LOH) at loci on three chromosomal arms (3p, 9p, and 17p) (Am J Path 1997;Vol151:Page323-Page327). Loss on these arms is a common event in oral epithelial dysplasia and has been associated with risk of progression of oral leukoplakia to cancer. The data showed that, although dysplastic epithelium demonstrated a high frequency of LOH (40% for mild dysplasia), a significantly lower frequency of LOH was noted in OLP (6%), which is even lower than that in hyperplasia (14%). Such results do not support OLP as a lesion at risk for malignant transformation. As a second step of the research, we determined LOH frequencies in 61 dysplastic lichenoid lesions (mild 35; moderate 19; severe 7) using the same microsatellite markers and compared these results with data obtained from the first study and from 13 normal mucosal specimens. Dysplastic lichenoid lesions showed a high frequency of loss (54% for lichenoid lesions with mild dysplasia), but values did not differ significantly from those observed in dysplasia of similar degree without lichenoid appearance. None of the normal mucosa demonstrated LOH. Epithelial dysplasia is a sign of malignant risk, independent of lichenoid changes. Such results suggest that pathologists should search for dysplasia carefully in lesions that otherwise qualify as OLP and that caution should be used when discounting dysplasia as being merely a reactive condition in lichenoid lesions.