ALDH1A1 and adenocarcinoma: In this context, particularly relevant was the study of Tiran and coworkers reporting the isolation from an adenocarcinoma lung patient resistant to chemotherapy of two tumorigenic cell populations, one initiated in spheroid cell cultures, with epithelial phenotype, expression of CSC markers (ALDH1, CD133) and the other one growing as adherent cells and characterized by positive expression for mesenchymal markers and negative expression for CSC markers [217].