Proliferation Activity in Pleomorphic Adenoma: Possible Prediction of Relapses

Pleomorphic adenoma (PA) is the commonest tumor of salivary glands. The tumor is benign, but the rate of tumor recurrences has been estimated up to 45% after simple enucleation and up to 5% after partial parotidectomy. There are no reliable histological criteria in PA indicating an increased risk of recurrence.
We decided to evaluate the significance of cell proliferation in primary PA for development of recurrence. Cell proliferation was studied by means of immunohistochemistry using monoclonal antibody MIB1 directed against cell cycle related antigen Ki-67. Salivary gland tumor registry yielded 670 PAs, and among these, 105 cases recurred. In a retrospective study we compared cell proliferation in myxoid and epithelial components of 50 cases of PAs with subsequent recurrence and of 50 cases of non-recurring PAs.
MIB1 proliferative indices in epithelial component of recurring PAs ranged between 0.1-10.6 (median 3.1) and of non-recurring PAs ranged between 0.1-3.0 (median 0.8). The MIB1 indices in myxoid component of recurring PAs were 0.0-4.0 (median 1.2) compared to those of non-recurring PAs 0.0-0.5 (median 0.2). The results were statistically significant (on the level of 5%). There was no statistical difference in proportion of epithelial and myxoid components of recurrent and non-recurrent PAs. However, much lower proportion of epithelial component was seen in recurrences (median 26%) than in primary PA (median 44 %). Proliferative activity as assessed by means of immunohistochemistry with MIB1 antibody in primary PA may help in predicting the risk of recurrences.

Keywords: salivary glands tumor; pleomorphic adenoma; recurrence; proliferative activity; prognosis; MIB1 index