Activated checkpoint kinase 2 expression and risk for oral squamous cell carcinoma

Abstract

Background: Phosphoactivation of a DNA damage response molecule checkpoint kinase 2 (pChk2) may be a marker of oral epithelial cells that have entered the precancerous and squamous cell carcinoma (SCC) stages. We explored whether there was selective expression of pChk2 in precancerous lesions but not in nonneoplastic tissue of the oral mucosa.

Experimental design: In a retrospective cohort design, 96 biopsied clinical leukoplakias and erythroplakias with known subsequent progression to SCC were identified from 48 subjects and assigned as the cases group. Expression status of pChk2 was compared with that of the 97 leukoplakias and erythroplakias that did not progress to SCC (control groups) by immunohistochemical analysis. Included in both groups were lesions with histologically confirmed dysplasia and those that lacked histologic evidence of atypia.

Results: Subjects with pChk2-positive but histology-negative (for atypia) lesions had an 8.6 times higher risk of developing SCC compared with those with pChk2-negative and histology-negative lesions. Overall, the presence of detectable pChk2 staining was able to identify lesions at risk of developing SCC within 3 years with a sensitivity of 85.2%, specificity of 74.2%, and predictive accuracy of 78.2% (odds ratio, 19.9; 95% confidence interval, 7.3-55.5).

Conclusion: This is the first study to include histologically nonatypical cases in the analysis of a putative biomarker for oral precancerous lesions. Our data show that pChk2 merits further investigation as a promising biomarker that can discriminate those lesions at risk for developing SCC, regardless of histologic evidence for atypia.

Figure 1

Photomicrographs of representative pChk2 immunostaining. A. Nuclear staining (brown) of the surface epithelium demonstrating considerable variation in the intensity of the stain within a given field. A diffuse staining pattern is observed (as opposed to sporadic and scattered positivity) involving full thickness of the epithelium. Magnification, ×100. B. A mitotic figure staining dark brown +3 intensity (short arrow), the golden brown staining (two arrowheads) is of +2 intensity,the lighter but discernable brown staining (two longer arrows) is of +1 intensity, and the faint brownish color (circle) was considered as background staining. A complete absence of brown stain (rectangle) was interpreted as negative staining. Magnification, ×400. The fraction of cells exhibiting nuclear staining of various intensity (0, +1, +2, and +3) was estimated and added together to formulate the cumulative score. For example, in the field shown ∼1% has +3 intensity, 15% with +2, and 30% with +1 intensity, which will yield (1% × 3) + two(15% × 2) + (30% × 1) = 0.63 cumulative score. Each slide was independently reviewed thrice and then the results between two pathologists compared to assure consistency.