Chromosome instability in lymphocytes: A potential indicator of predisposition to oral premalignant lesions

Oral premalignant lesions (OPLs) are related to tobacco use and mark individuals at high risk for oral cancer development. Increased mutagen sensitivity as measured by an in vitro mutagen challenge assay has been shown to he a risk factor for upper aerodigestive tract cancers. In this case control study, we used two assays with mutagens relevant to tobacco exposure (benzo[a]pyrene diol epoxide (BPDE) and bleomycin) to see whether sensitivity to these mutagens could be used as biomarkers for assessing risk of premalignant lesions. Furthermore, we evaluated whether 3p21.3 is a molecular target of BPDE damage in lymphocytes of patients with OPLs. There were 82 patients with OPLs and 89 healthy controls frequency matched to the cases on age, sex, ethnicity, and smoking status. These subjects' lymphocytes were treated in two separate experiments with either 2 μM BPDE for 24 h or 0.03 units/ml bleomycin for 5 h, and the frequency of induced chromatid breakage in Giemsa-stained preparations was determined. BPDE-induced 3p21.3 aberrations were scored by fluorescent in situ hybridization technique in 1000 interphases/sample. We found that the mean BPDE-induced chromatid breaks per cell were higher in cases than controls (1.05 ± 0.40 and 0.55 ± 0.27, respectively; P < 0.01). Similar results were evident with bleomycin-induced chromatid breaks per cell (0.78 ± 0.37 and 0.57 ± 0.31, respectively; P < 0.01). After adjusting for age, sex, ethnicity, and smoking status, significantly elevated odds ratios (95% confidence interval) for OPL risk were noted for BPDE sensitivity [12.96 (5.51, 30.46)] and bleomycin sensitivity [3.33 (1.64, 6.77)]. When subjects were categorized into quartiles of the number of breaks per cell, a dose response was observed for both assays. The adjusted odds ratios for subjects with increasing numbers of breaks per cell in quartiles were 2.34, 9.14, and 54.04 for BPDE sensitivity and 1.92, 3.33, and 7.15 for bleomycin sensitivity, respectively. Subjects sensitive to both mutagens had a 50-fold increased risk for OPLs. In addition, there were significantly more BPDE-induced chromosome aberrations at the 3p21.3 locus in cases (51.13/1000) than in controls (40.93/1000; P < 0.0001). However, no such difference was observed for 3q13, a control locus. BPDE-induced 3p21.3 aberrations were associated with an elevated risk for OPLs of 6.08 (2.57, 14.4). The degree of BPDE sensitivity at 3p21.3 and risk for OPLs increased in a dose-dependent manner. In summary, BDPE sensitivity and bleomycin sensitivity appear to be individually and jointly associated with elevated risk of OPLs, Furthermore, 3p21.3 may be a molecular target of BPDE in OPLs. This is the first study to examine mutagen sensitivity in a premalignant condition. The next step is to correlate these findings in surrogate (lymphocyte) tissue with molecular events in the target tissue.