Immunohistochemical expression of 8-oxo-7,8-dihydro-2′-deoxyguanosine in cytoplasm of tumour and adjacent normal mucosa cells in patients with colorectal cancer

BACKGROUND The aim of this research was to study the levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in tumour tissue samples of colorectal carcinoma based upon immunohistochemical detection and compare those results with patients' outcome. METHODS Tumour blocks of patients surgically treated for colorectal cancer were evaluated by 8-oxodG immunohistochemical staining. The expression was analysed in 500 tumour cells. The percentage of positive cells, as well as staining intensity, was recorded, and Allred score was calculated. For each patient, data of age, gender, tumour size and location, margin status, histologic grade, tumour stage, lymph node status, vascular invasion, overall survival, and therapy protocols were collected. Tumour grade was divided into two groups as low and high grade. RESULTS In this study, 146 consecutive patients with primary colorectal carcinoma were included. All data were available for 138 patients, and they were included in this research. There were 83 male and 55 female patients; the median age was 64 years (range 35-87 years). The results showed shorter 5- and 10-year survival in patients with 8-oxodG positive tumour cells (5-year survival, n=138, Mantel-Cox, chi-square 4.116, degree of freedom (df)=1, p<0.05; 10-year survival, n=134, Mantel-Cox, chi-square 4.374, df=1, p<0.05). The results showed a positive correlation between Allred score and high tumour grade (two-tailed Spearman's ρ 0.184; p<0.05), as well as with non-polypoid tumour growth (two-tailed Spearman's ρ 0.198; p<0.05). There was no significant difference of 8-oxodG expression related to age, sex, blood group, size and tumour site, distance from the edge of the resected tumour margin, lymph nodes involvement, and vascular invasion. CONCLUSIONS In this study, the positive correlation between 8-oxodG presence in the tumour cells, worse clinical outcome, higher tumour grade, and flat morphology was found.