Immunohistochemical pattern of Bcl-2- and PTHrP-positive cells in primary, in recurrent and in carcinoma in pleomorphic adenomas

Summary Forty-seven samples o f paraffin-embedded formalinfixed (and 2S related frozen) sections o f 27 primary pleomorphic adenomas, 1S recurrent pleomorphic adenomas and S carcinomas in pleomorphic adenomas were studied to analyse their immunohistologic patterns with respect to the ratio o f the expression o f ‘normally’ and ‘aberrantly’ differentiated cell types. In primary pleomorphic adenoma PTHrP-positive cells are seen in the inner layer o f tubulo-ductal structures, in part o f the cells in the mucoid, chondroid, or myxochondroid matrix, and in the squamous metaplastic areas. Bcl-2-positive cells are found in the outer layer o f tubulo-ductal structures, in part of the cells in the mucoid, chondroid, or myxocbondroid matrix, and around the squamous metaplastic areas. In one case o f primary pleomorphic adenoma, which recurred later, the positivity for Bcl-2 is more intense and seen in the periphery o f this tumour with a predominantly myxoid pattern. In recurrent pleomorphic adenomas, which also mostly showed a predominantly myxoid pattern, the positivity for Bcl-2 showed a pattern similar to the primary-to-recur tumour. PTHrP-positive cells are found less frequently than Bcl2-positive cells. In carcinoma in pleomorphic adenoma, the benign part shows the features o f primary pleomorphic adenoma with its Bcl-2 and PTHrP-positivity patterns. The malignant part strongly shows Bcl-2-positive cells in the periphery o f the tumour. We conclude that the maintained presence o f Bcl-2 and PTHrP-positive cells in the tumours we studied shows the variable capacity of tumour cells to differentiate.