The cytokine interferon-alpha (IFN alpha) belongs to the group of type I interferons already used in cancer therapy. This drug possesses radio- and chemo-sensitizing, and shows anti-angiogenic properties. Cancer stem cells (CSC) are a unique population of tumor cells that initiate secondary tumors, and are responsible for metastasis formation. Patients with pancreatic ductal adenocarcinoma (PDAC) have an especially poor prognosis, with 5-year survival rates of only similar to 1% and median survival of 4-6 months. PDAC is characterized by the presence of CSC. In this work we demonstrate for the first time that IFN alpha up-regulates the expression of the CSC markers CD24, CD44 and CD133 in in vitro and in vivo models of PDAC. We showed the IFN alpha effects on the migration and invasion of PDAC cells, which is associated with the level of the CSC marker expression. In vivo, this drug inhibits tumor growth but promotes metastasis formation in the early stage of tumor growth. We propose that IFN alpha may enhance the enrichment of CSC in PDAC tumors. Additionally we also suggest that in combination therapy of solid tumors with IFN alpha, this drug should be given to patients prior to chemotherapy to achieve the CSC activation. (C) 2014 Elsevier Inc. All rights reserved.