ERCC2 and head and neck squamous cell carcinoma: BRCA2 and XPD proteins were significantly (p < 0.0001) downregulated in the PBL of HNSCC patients to 71% and 77% the levels in controls, showing significant negative correlation with HNSCC stage (Spearman correlation coefficient (rs) of −0.9060, p < 0.0001 for BRCA2; rs of −0.8008, p < 0.01 for XPD).