Fig 2: ALDH1, BCL11B, BMI-1, and CD44 expression in head and neck squamous cell cancer (HNSCC) and distribution in the two study cohorts. Shown are examples of ALDH1 (a), BCL11B (b), BMI-1 (c), and CD44 (d) expression ranging from none (0), weak (1), and intermediate (2) to strong (3) in HNSCC (200 ×). ALDH1, BCL11B, BMI-1, and CD44 staining is red-brown, while nuclei and cytoplasm are counter-stained with hemalaun (blue). e Immunohistochemistry (IHC) scores combine proportions and intensities of staining as described in “Material and methods” for the four reported stem cell markers ALDH1 (cytoplasmic expression), BCL11B (nuclear), BMI-1 (nuclear), and CD44 (cytoplasmic). Per definition, IHC scores could reach values between 0 and 300. The plots reflect the frequency distribution of the IHC scores

Fig 3: Association of single ALDH1, BCL11B, BMI-1, and CD44 immunohistochemistry scores with clinical outcome in the human papillomavirus (HPV)-stratified primary radio(chemo)therapy (pRCT) subcohorts. Kaplan-Meier curves for overall survival (OS), disease-free survival (DFS), and disease-specific survival (DSS) in head and neck squamous cell carcinoma patients stratified into groups with low and high expression of ALDH1, BCL11B, BMI-1, and CD44. p-Values (log-rank test) and the applied optimized threshold for the classification of patient subgroups are indicated for the HPV-positive subcohort (a) and the HPV-negative subcohort (b)