KRAS-mutation positive, metastatic tonsil carcinoma with cancer stem-like cell features and long-term response to gefitinib: a case report and review of the literature - Gottschling, Sandra; Penzel, Roland; Pelz, Tanja; Herpel, Esther; Schnabel, Philipp Albert; Dyckhoff, Gerhard; Thomas, Michael; Kuhnt, Thomas (Journal of clinical oncology. [Englische Ausgabe], 2011)