Downregulation of ALDH1A1 expression in non-small cell lung carcinomas--its clinicopathologic and biological significance.

ALDH1A1 metabolizes a variety of endogenous and exogenous aldehyde, and also oxidizes retinol to synthesize retinoic acid and modulate cell differentiation. Moreover, ALDH1A1 is also suggested to participate in the maintenance of cancer stem cells. To investigate the potential role of ALDH1A1 in carcinogenesis of the lung, the present study examined two hundred and sixty eight cases of non-small cell lung carcinoma (NSCLC) for its immunohistochemical expression and analyzed associations between ALDH1A1 levels and a series of clinicopathologic parameters. Also, the biological significance of the aberrant expression of ALDH1A1 was investigated in vitro. ALDH1A1 expression was markedly reduced in 39.9% (107/268) of NSCLCs. The incidence of this reduction was significantly higher in adenocarcinomas (ADC: 41.6%, 85/207) and large cell carcinomas (61.1%, 11/18) than squamous cell carcinomas (25.5%, 11/43). Among ADCs, the downregulation tended to be more remarkable in high grade, poorly differentiated tumors, and tumors with stronger proliferating activity. It also occurred with a significantly higher incidence in smokers than non-smokers. Forced expression of ALDH1A1 in NSCLC cell lines, which had lost ALDH1A1 expression, markedly attenuated their growth. Taken together, loss of ALDH1A1 expression is suggested to promote carcinogenesis especially in the smoking-related ADCs.