Role of endometriosis in cancer and tumor development.

Endometriosis, like cancer, is characterized by cell invasion and unrestrained growth. Furthermore, endometriosis and cancer are similar in other aspects, such as the development of new blood vessels and a decrease in the number of cells undergoing apoptosis. In spite of these similarities, endometriosis is not considered a malignant disorder. The possibility that endometriosis could, however, transform and become cancer has been debated in the literature since 1925. Mutations in the genes that encode for metabolic and detoxification enzymes, such as GALT and GSTM, have been implicated in the pathogenesis of endometriosis and in the progression to carcinoma of the ovary. PTEN, a tumor suppressor commonly mutated (50%) in endometrial carcinoma, is found mutated in endometrioid carcinoma of the ovary, but not in other forms of ovarian cancer. A recent study has shown that somatic mutations in the PTEN gene were identified in 20% of endometrioid carcinomas and 20.6% of solitary endometrial cysts, suggesting that inactivation of the PTEN tumor suppressor gene is an early event in the development of ovarian endometrioid carcinoma. In addition to cancerous transformation at the site of endometriosis, there is recent evidence to indicate that having endometriosis itself may increase a woman's risk of developing non-Hodgkin's lymphoma, malignant melanoma, and breast cancer.