Cancer stem cell marker ALDH1 expression is associated with lymph node metastasis and poor survival in esophageal squamous cell carcinoma: a study from high incidence area of northern China

Tumor recurrence and metastasis is the leading cause of death in esophageal squamous cell carcinoma (ESCC). Cancer stem cell (CSC) may be responsible for tumor growth and maintenance of aggressive behavior. Aldehyde dehydrogenase 1 (ALDH1) has been proposed as one of the possible candidates for a CSC marker. The expression of ALDH1 may be correlated with the clinicopathologic factor and clinical outcome of patients with ESCC. The purpose of this study was to investigate the expression of ALDH1 protein in human ESCC tissues, and evaluated the clinical implication of ALDH1 expression for these patients. All 79 patients who underwent esophagectomy for ESCC between January 2005 and June 2006 were enrolled in this study. The expression of ALDH1 in ESCC and adjacent noncancerous tissues was analyzed by immunohistochemistry. ALDH1 was mainly expressed in ESCC cell nucleus. For the 79 ESCC patients, increased nuclear accumulation of ALDH1 was found in 12 (15.2%) specimens. ALDH1 expression was correlated with poor histological differentiation (P= 0.003), lymph node metastasis (P= 0.011), and late pathologic TNM classification (pTNM) staging (P= 0.003). Patients in ALDH1 positive group had a significantly poor 5-year overall survival than those in the negative group (8.3% vs. 52.2%, P= 0.025). We have demonstrated for the first time that the CSC marker, ALDH1, is expressed in human ESCC. The expression of ALDH1 protein in nucleus of the ESCC is significantly associated with lymph node metastasis and poor survival. Our results highly indicate the involvement of ALDH1 in the aggressive behavior of ESCC.