['Despite significant advances in the use of diagnosis and therapy to treat head and neck squamous cell carcinoma (HNSCC), the prognosis has improved only marginally in the last decades. Thus, there is an enormous need for better understanding of tumor biology and reversely novel immunotherapeutic approaches. It is becoming increasingly obvious that stem cells play an important role in tumor development and progression. The identity of these cells and the underlying cellular and molecular mechanisms are mostly unknown in HNSCC to date.', 'Solid HNSCC tumors, as well as permanent HNSCC cell lines, were analyzed by flow cytometry concerning the expression of different putative stem cell marker proteins.', 'Distinct populations of CD44 expressing potential stem cells could be identified in solid tumors of HNSCC patients with strong individual deviations. Surprisingly, the potential stem cell marker CD44 was found to be constitutively expressed on the surface of all the permanent HNSCC cell lines analyzed.'] Is potential stem cell marker CD44 constitutively expressed in permanent cell lines of head and neck cancer?