Malignancy in Pleomorphic Adenoma: A Clinical and Microspectrophotometric Study

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Abstract
A clinical study of carcinoma in pleomorphic adenoma, based on the most extensive material described in the literature hitherto, strongly indicates that a malignant transformation of a primarily benign pleomorphic adenoma may occur and that the risk of such transformation increases with the age of the tumour (the preoperative duration of the tumour). A microspectrophotometric DNA analysis shows a difference in the DNA content between morphologically benign pleomorphic adenomas with short and with long preoperative duration of the tumour. As cells from pleomorphic adenomas with a short preoperative duration contain the same diploid DNA value as normal parotid gland cells, the pleomorphic adenomas with a longer preoperative duration are characterized by the occurrence of a small fraction of tetraploid cells in the population. This small fraction of tetraploid cells may be of great importance for the development of malignancy in these tumours, as it was found that the cases of carcinoma in pleomorphic adenoma also have a tetraploid (or near tetraploid) fraction of cells. It is tempting to suggest that the tetraploid cells of the carcinoma in pleomorphic adenoma have originated from the tetraploid cells occurring in benign pleomorphic adenomas with prolonged clinical course. The present clinical and microspectrophotometric study indicates the importance of an early operation even of the benign pleomorphic adenomas, as the risk of malignant transformation of this type of tumour has been shown to increase with the preoperative duration of the tumour.