Low level of BRCA2 in peripheral blood lymphocytes is associated with an increased risk for head and neck squamous cell carcinoma (HNSCC) in a population of North-East India: a case-control study

BACKGROUND: We investigated the role of DNA repair proteins breast cancer susceptibility 2 (BRCA2), xeroderma pigmentosum group D (XPD) and apurinic/apyrimidinic endodeoxyribonuclease 1 (APE1) in determining the risk for head and neck squamous cell cancer (HNSCC) in a case-control study from North-East India. METHODS: Expression of BRCA2, XPD and APE1 genes in the matched tumour, normal adjacent tissue (NAT) and blood of 12 HNSCC patients and blood of 8 age- and gender-matched controls was determined by quantitative real-time PCR. Results were validated by expression analysis of the corresponding proteins in the peripheral blood lymphocytes (PBLs) of 228 subjects (106 patients and 122 controls) by a slot-blot immunoassay. FINDINGS: Expression of the BRCA2 and XPD genes in tumour tissue of HNSCC patients declined progressively as the cancer stage advanced, was reverse that of the NAT, but was mirrored by the expression in the blood. 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 (r(s)) of −0.9060, p < 0.0001 for BRCA2; r(s) of −0.8008, p < 0.01 for XPD). On the contrary, APE1 was significantly upregulated in PBL of HNSCC patients to 1.47 fold the level in controls, showing significant positive correlation with HNSCC stage (r(s) of 0.7023, p < 0.01). Classification and regression tree analyses predicted low levels of BRCA2 protein in PBL as the single most important risk factor for HNSCC, independent of gender. Smokers above 36 years of age with low level of BRCA2 appeared to exhibit a 1.78-fold increased risk for HNSCC (with a 1.78-fold increased risk for HNSCC (OR = 1.78, 95% confidence interval (CI) = 0.33–9.52) though this risk was not significant statistically. Similarly, low levels of BRCA2 appeared to indicate a moderate, but non-significant risk for HNSCC in non-smokers aged between 36 and 56 years (OR = 1.15, 95% CI = 0.21–6.37). CONCLUSIONS: Low level of BRCA2 protein in the peripheral blood indicates increased risk for HNSCC.