Polycyclic aromatic hydrocarbon exposure in oesophageal tissue and risk of oesophageal squamous cell carcinoma in north-eastern Iran

Abstract

Objective: To evaluate the association between polycyclic aromatic hydrocarbon (PAH) exposure in oesophageal epithelial tissue and oesophageal squamous cell carcinoma (ESCC) case status in an ESCC case-control study in a high-risk population in north-eastern Iran.

Methods: Tissue microarrays (TMAs) of non-tumoral oesophageal biopsies from patients with biopsy-proven ESCC and gastrointestinal clinic patients with no endoscopic or biopsy evidence of ESCC (control subjects) in a rural region in north-eastern Iran were immunohistochemically stained. Immunohistochemistry was performed using monoclonal antibodies 8E11 and 5D11 raised against benzo[a]pyrene (B[a]P) diol epoxide (BPDE)-I-modified guanosine and BPDE-I-modified DNA, respectively. Staining intensity was quantified by image analysis and the average staining in three replicates was calculated. The main outcome measure was adjusted ORs with 95% CIs for the association between antibody staining intensity and ESCC case status.

Results: Cultured ESCC cells exposed to B[a]P in vitro showed dose-dependent staining with 8E11 but not with 5D11. With 8E11, sufficient epithelial tissue was available in the TMA cores to analyse 91 cases and 103 controls. Compared with the lowest quintile of 8E11 staining in the controls, adjusted ORs for the 2nd to 5th quintiles were 2.42, 5.77, 11.3 and 26.6 (95% CI 5.21 to 135), respectively (p for trend <0.001). With 5D11, 89 cases and 101 controls were analysed. No association between staining and case status was observed (ORs for the 2nd to 5th quintiles were 1.26, 0.88, 1.06 and 1.63 (95% CI 0.63 to 4.21), p for trend=0.40).

Conclusions: Dramatically higher levels of 8E11 staining were observed in non-tumoral oesophageal epithelium from patients with ESCC than from control subjects. This finding strengthens the evidence for a causal role for PAHs in oesophageal carcinogenesis in north-eastern Iran.

Figure 1

Immunostaining of the TE6 squamous cell carcinoma cell line with 8E11 and 5D11 antibodies. With 8E11, unexposed cells show no evidence of staining, and staining increases in a dose-dependent manner with increasing exposure to B[a]P. With 5D11, background nuclear staining is seen in the unexposed cells, and there is no clear dose-dependent increase in staining with increasing B[a]P exposure.

Figure 2

Immunostaining of the TMA cores with the 8E11 antibody. Figures A–C (400x) show a spectrum of increasing staining intensity; the staining is predominantly cytoplasmic and involves the full thickness of the epithelium. Figure D (200x) shows full-thickness staining with sparing of the basal cells around the vascular papillae.