['Aldehyde dehydrogenase 1 (ALDH1) has been identified as a reliable marker of breast cancer stem cells. The aim was to determine the prognostic significance of ALDH1 expression in a long-term follow-up study.', "Immunohistochemical analyses were performed on 257 invasive ductal carcinomas (IDCs), 109 matched lymph node metastases and 190 ductal carcinomas in situ (DCISs), using paraffin-embedded sections. ALDH1 expression was found in 26% of IDCs, and correlated with larger tumour size (P=0.007), high histological grade (P<0.001), HER2 overexpression (P<0.001) and negative hormone receptor status (P<0.001). ALDH1 expression was observed in 14% of DCISs but was not correlated with any clinicopathological parameter. The IDC patients were followed up for 7-190 months (median: 120 months), and groups with ALDH1 expression had shorter relapse-free survival (P=0.0013) and overall survival (OS) (P=0.0005) by log-rank test. By Cox's multivariate analysis, it had a weak effect on OS (P=0.047), and its most significant effect on OS was observed in node-positive groups (P=0.013). No significant differences in OS stratified by ALDH1 expression status in lymph node metastases were noted."] Is aldehyde dehydrogenase 1 expression a predictor of poor prognosis in node-positive breast cancers : a long-term follow-up study?