Mutations associated with carcinomas arising from pleomorphic adenomas of the salivary glands

Pleomorphic adenoma (PA) is the most common benign tumor of salivary glands. Carcinomas in pleomorphic adenomas (CPAs) may arise by malignant transformation of the epithelial components of PAs. Occasionally, transitional zones containing cells with histological features intermediate between those of the benign PA and carcinomatous components of CPA are identified. After careful microdissection of archival microslides, the authors studied 12 cases of CPAs and their attendant adenomatous and transitional areas for mutations in the p53, RB, and K-ras genes, and at chromosomal loci 5q and 9p. The authors failed to find mutations in the K-ras gene or 9p locus. A relatively high rate of mutations (loss of heterozygosity [LOH] and microsatellite alterations) at the p53 gene were detected in CPAs (58%), and at somewhat lower frequencies at the RB gene (33%) and chromosomal location 5q (17%). Mutational frequency in the associated transitional and adenomatous areas were slightly lower than in the corresponding CPAs. No mutations were detected in adenomatous or transitional areas unless they also were present in the corresponding CPAs. Mutations of these three genes were absent in four cases of CPA, and in seven PAs without malignant change. These findings indicate that most CPAs arise from adenomas as the result of mutations in the three genes, especially p53. In addition, other, as yet unidentified genes may also be involved both in the development of PA and in its malignant progression to CPA. Mutational analysis of PAs may provide information of prognostic importance.