[An approach to early genetic alterations in precancerous cells]

To investigate the potential role of the PTEN tumor-suppressor gene in the carcinogenesis of ovarian endometrioid carcinoma and its related subtype, clear cell carcinoma, we examined 20 ovarian endometrioid carcinomas, 24 clear cell carcinomas and 34 solitary endometrial cysts of the ovary for LOH at 10q23.3 and point mutations of the PTEN gene, using a laser-assisted microdissection method. LOH was found in 8 of 19 ovarian endometrioid carcinomas (42.1%), 6 of 22 clear cell carcinomas (27.3%) and 13 of 23 solitary endometrial cysts (56.5%). Somatic mutations in the PTEN gene were identified in 4 of 20 ovarian endometrioid carcinomas (20.0%), 2 of 24 clear cell carcinomas (8.3%) and 7 of 34 solitary endometrial cysts (20.6%). In 5 endometrioid carcinomas with endometriosis, 3 displayed LOH events common to both the carcinoma and the endometriosis. In 7 clear cell carcinomas with endometriosis, 3 displayed LOH events common to both the carcinoma and the endometriosis. In no cases there were LOH events in the endometriosis only. These results indicate that inactivation of the PTEN gene is an early event in the development of both endometrioid and clear cell carcinoma of the ovary. A laser-assisted microdissection method enables us to collect target cells without contamination by non-tumor cells. We expect that this technique will be very useful for investigating genetic alterations in cancerous or precancerous lesions. Early genetic alterations in various precancerous cells detected by light microscopy can be readily identified by the tissue-microdissection method.