Background: The origin of recurrences of pleomorphic adenomas after initial surgical treatment is discussed. In this study mesenchymal and epithelial tumorcomponents were immunhistochemically stained in recurrent and nonrecurrent adenoma. In addition the proliferation activity was assessed.
Methods: Twelve nonrecurrent adenomas (10 of the parotid gland, 2 of the submandibular gland) and 18 recurrent adenomas (15 of the parotid gland, 3 of the submandibular gland) were immunhistochemically stained with a MIB1 antibody against the cell proliferation associated nuclear antigen (Ki-67 antigen). The proliferation index (MIB1 positive cells per 100 cells) was calculated separately for each tumor component.
Results: The mean value (x) of the proliferation indices of the component with epithelial differentiation was 4.67 (recurrent group, standard deviation [SD]: 3.14) and x = 2.34 respectively (nonrecurrent group, SD = 1.83). The difference between the mean values was significant (p = 0.028). For the component with mesenchymal differentiation the values were x = 0.33 (for recurrent adenomas, SD = 0.59) and x = 0.17 (nonrecurrent adenomas, SD = 0.39) respectively. The difference was not significant.
Conclusions: Proliferation activity is markedly higher in components with epithelial differentiation of recurrent adenomas compared to nonrecurrent tumors. The results demonstrate the tumor component with epithelial differentiation as a possible origin for recurrence.