Molecular analysis of clonality in ovarian endometrial cysts.

Ovarian endometrial cysts, one of the typical manifestations of endometriosis, are classified as tumor-like lesions rather than as neoplasms. Clonality analysis provides important information on the histogenesis and progression of neoplastic diseases. It is generally accepted that most neoplasms are monoclonal in origin, while the clonality of endometrial cysts remains uncertain. In our study, the clonality of endometrial cysts was analyzed by means of polymerase chain reaction (PCR) based on restriction fragment length polymorphism of the X chromosome-linked human androgen receptor gene (HUMARA) and on random inactivation of the gene by methylation. We separated 21 fresh epithelial cell samples from 11 endometrial cysts and found that all were monoclonal in the methylation pattern of the human androgen receptor alleles. Moreover, in each of the five cysts where epithelial cells were sampled from multiple areas, the methylation patterns of all samples from a single cyst were identical. These data indicate that endometrial cysts are monoclonal in origin and suggest their neoplastic potential.