APEX1 and head and neck squamous cell carcinoma: On the basis of our earlier findings, we hypothesised that another crucial effector of the HR pathway, breast cancer susceptibility 2 (BRCA2), along with the XPD and APE1 protein of the NER and BER pathways, respectively, may play a vital role in determining the risk for HNSCC in association with tobacco use, in the population of the region.