Moreover, due to the invasiveness of tissue biopsies, the difficulties posed for repeated sampling and the unavailability of large number of tissue biopsies, we have emphasised on evaluating the expressions of BRCA2, XPD and APE1 in the PBL of HNSCC patients and control individuals, using slot blot technique for validating our result on a larger sample size. The gene discussed is APEX1; the disease is head and neck squamous cell carcinoma.