Retinoic acid receptor-β expression in stage I non-small cell lung cancer and adjacent normal appearing bronchial epithelium

Retinoic acid receptor-beta (RAR-beta) is induced by and mediates the growth-inhibitory and apoptotic effects of retinoic acid (RA), suggesting that loss of RAR-beta expression may be one of the critical events involved in the carcinogenesis/progression of non-small cell lung cancer (NSCLC) and in the responsiveness to retinoid chemotherapy. However, recent contradictory reports that the expression of RAR-beta is associated with poor clinical outcome, and the fact that treatment of serum-deprived type 2 alveolar cells with RA leads to a stimulation of cell proliferation, require the verification of RAR-beta as a biomarker of chemoprevention or prognosis. The expression status of RAR-beta in cancer cells and adjacent normal appearing bronchial epithelium from 39 patients, diagnosed as stage I NSCLC and undergone a curative lung resection, was analyzed in paraffin-embedded tissue sections by IHC staining. The normal appearing bronchial epithelium of 14 out of 33 (42.4%) specimens expressed RAR-beta, whereas 22 out of the 39 (56.4%) stage I NSCLC specimens expressed RAR-beta. RAR-beta was more frequently expressed in the adenocarcinoma (72.7%) than in the squamous cell carcinoma (31.3%) (p=0.026). Neither the expression status in normal appearing adjacent tissue nor that in the tumor tissue had prognostic implications. The higher expression of RAR-beta in cancer tissue, the focal and uneven distribution in normal appearing adjacent bronchial epithelium, and inconsistency with the corresponding tumor tissue, suggest that the expression status of RAR-beta as a biomarker for chemoprevention/early diagnosis or the prognosis of NSCLC requires further consideration.