ALDH1 Expression and the Prognosis of Lung Cancer: A Systematic Review and Meta-Analysis.

Aldehyde dehydrogenase 1 (ALDH1) has been identified as a putative cancer stem cell (CSC) marker in lung cancer. However, the clinicopathological and prognostic value of this protein in lung cancer patients remains controversial. Thus, we performed a systematic review and meta-analysis of studies assessing the clinical and prognostic significance of ALDH1 expression in lung cancer.An identification and review of publications assessing clinical or prognostic significance of ALDH1 expression in lung cancer until September 1, 2014 was undertaken. A meta-analysis was performed to clarify the association between ALDH1 expression and clinical outcomes.A total of 14 publications met the criteria and comprised 1926 cases. Analysis of these data showed that ALDH1 expression was not significantly associated with the patient age (OR = 0.82, 95% confidence interval [CI]: 0.45-1.50, P=0.52), tumour size (OR=0.68, 95% CI: 0.22-2.06, P=0.49), smoking status (OR=1.37, 95% CI: 0.85-2.22, P=0.19), or tumour grade (OR=1.65, 95% CI: 0.83-3.26, P=0.15). However, in the identified studies, ALDH1 expression was highly correlated with lymph node metastasis (OR=1.97, 95% CI: 1.16-3.34, P=0.01), tumour TNM staging (OR=1.68, 95% CI 1.28-2.22, P=0.0002), decreased overall survival (relative risk [RR]: 1.97,95% CI: 1.16-3.34, P =0.01) and decreased disease free survival (RR: 1.63, 95% CI: 1.01-2.64, P=0.05).This meta-analysis shows ALDH1 expression in lung cancer is connected with decreased overall and disease free survival and thus marks a worse prognosis.