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Background: Retinoids are effective in the treatment and prevention of certain human cancers. Most of their actions are thought to result from changes in gene expression mediated by nuclear retinoic acid receptors and retinoid X receptors. We conducted a study to determine whether the expression of these receptors was altered in premalignant oral lesions and, if so, whether their expression could be restored by treatment with isotretinoin. Methods: We performed in situ hybridization of retinoic acid receptors and retinoid X receptors using antisense riboprobes in specimens of oral mucosa from 7 normal subjects and specimens of premalignant oral lesions from 52 patients before treatment with isotretinoin and from 39 of the 52 patients after three months of treatment. Results: All the normal specimens expressed retinoic acid receptor–β messenger RNA (mRNA). In contrast, retinoic acid receptor–β mRNA was detected in only 21 of the 52 premalignant oral lesions (P = 0.003). Thirty-five of the 39 specimens available for evaluation after treatment expressed retinoic acid receptor–β mRNA (P<0.001). All normal and premalignant specimens expressed similar levels of mRNA for retinoic acid receptor–α and retinoic acid receptor–γ and the three types of retinoid X receptors, α, β, and γ. The levels of retinoic acid receptor–β mRNA increased in the specimens from 18 of the 22 patients who had responses to isotretinoin and in 8 of the 17 specimens from the patients without responses (P = 0.04). Conclusions: The expression of retinoic acid receptor–β mRNA is selectively lost in premalignant oral lesions and can be restored by treatment with isotretinoin. Restoration of the expression of retinoic acid receptor–β mRNA is associated with a clinical response. Retinoic acid receptor–β may have a role in mediating the response to retinoids and may be a useful intermediate biologic marker in trials of these agents for the prevention of oral carcinogenesis. (N Engl J Med 1995;332:1405-10.) [ABSTRACT FROM AUTHOR]