HLA-C and head and neck squamous cell carcinoma: However, compared to the training cohort and independent validation cohort of our earlier investigation (11, 12), HLA-C homozygosity was the only HLA trait demonstrating a lower frequency in HPV-driven HNSCC (20.2% versus 30.3%; p = 0.093), whereas all other frequencies of particular HLA traits were not different (all p > 0.22).