Immunohistochemical staining and analysis of human patient material was performed on tissue microarrays (TMA) as previously described(80 (link)). All tissues analyzed in this study were obtained from patients at the Institute of Surgical Pathology, University Medical Center Freiburg, Germany. This study was approved by the Ethics Committee of the University Medical Center Freiburg (no. EK 10/12). The patient cohort (n=375) comprised adenocarcinomas (n=186) and squamous cell carcinomas (n=189). Where required, histological diagnoses were verified according to current WHO classification with immunohistochemistry(81 (link)). The maximum follow-up time was 210 months. Clinical data comprising pTMN, resection status (R), gender and patient age at diagnosis are summarized in Table S15. Immunohistochemical staining was performed on a Discovery XT automated stainer (Ventana) using the following primary antibodies: MELK (1:50, Sigma-Aldrich), DDR1 (1:50, Biozol), and EGFR (pharmDx™-kit, DAKO). Signal detection was performed using peroxidase-DAB (diaminobenzidine)-MAP kit (Roche, Ventana). The immunohistological expression of the membrane-binding EGFR, the nuclear MELK and the cytoplasmatic DDR1 were classified into four levels according to specific staining intensity: Score 0, 1+, 2+, 3+.