Somatic mutations of the PTEN tumor suppressor gene in sporadic follicular thyroid tumors

The PTEN (MMAC1/TEP1) tumor suppressor gene was recently isolated and mapped to human chromosome band 10q23. Homozygous deletions and mutations of PTEN were observed in cell lines and sporadic cancers of the breast, kidney, and central nervous system. Germline mutations in PTEN were recently found in Cowden disease, an autosomal dominant inherited syndrome, previously mapped to chromosome bands 10q22-23. This disease is associated with a wide variety of malignancies and hamartomas of ectodermal, mesodermal, and endodermal origin. The most common neoplasms in Cowden disease patients arise in the breast, skin, and thyroid (follicular subtype). To determine the involvement of PTEN in sporadic follicular thyroid tumors, we first analyzed sporadic follicular adenomas and carcinomas for deletions of the PTEN gene. Loss of heterozygosity was found in 7/26 (27%) follicular carcinomas and 2/27 (7%) follicular adenomas, one of which was a small hemizygous deletion (~3 cm). Sequence analysis of the entire PTEN coding region revealed two mutations in carcinomas with 10q loss. Our findings suggest that the PTEN tumor suppressor gene is occasionally inactivated in sporadic follicular thyroid tumors.