Cell kinetics characterization of pleomorphic adenoma of the parotid gland

IDEA The pleomorphic adenoma of the parotid gland is a benign lesion characterized by histomorphologic heterogeneity. However, irrespective of the histologic aspect, local recurrence occurs in 10-12% of cases and malignant transformation is not uncommon. So far, the biological pattern of these neoformations have poorly investigated. The aim of the present study was to characterize the proliferative activity of the pleomorphic adenoma by assessing nuclear DNA content and Proliferating Cell Nuclear Antigen (PCNA). METHOD In serial 5-micron-thick paraffin sections of 25 parotid adenomas DNA content and PCNA positivity were evaluated by densitometry and by immunohistochemistry respectively. DNA content was measured with a Zeiss VIDAS image analyzer. The integrated optical density was estimated on parotid nuclei stained with Feulgen's method. For PCNA characterization, the sections were immunostained with the monoclonal antibody PC10, using an immunoperoxidase method (ABC complex). RESULTS The histograms obtained with densitometric method showed different percentages of cells with 2C, 3C and 4C DNA content and different DNA-index values (range=0.97-1.65; mean value=1.24). The PCNA index showed considerable variability with values ranging from 3.7% to 53.9% (mean value=23.38 %). It was possible to distinguish two types of adenoma. In Group I there was a prevalence of diploid cells with a low PCNA index. Group II was represented by adenomas with a large percentage of triploid cells and a PCNA index significantly higher than that of Group I. CONCLUSION On the basis of the findings of our study on DNA content and PCNA index, we were able to identify two groups of parotid pleomorphic adenoma which, though histologically superimposable, were distinguished by a different proliferative cell profile. These results suggest that the possibility of recurrence or malignant transformation depends on intrinsic biological properties of each adenoma.