Malignant transformation in extra-ovarian endometriosis is a rare but known complication. This distinct pathological entity is reviewed with a specific focus on aetiology and treatment.

Studies were identified by searching the English language literature in the MEDLINE database and by an extensive review of bibliographies from articles found through that search.

Up to 1% of women with endometriosis will develop endometriosis-associated neoplasm. Almost a quarter of the reported cases of malignancy in endometriosis have involved extra-ovarian tissues. In many cases, hormonal factors may play a role in its pathogenesis. Estrogen monotherapy in obese patients significantly increase the risk of malignant extra-gonadal endometrial transformation. Genetic anomalies have also been reported such as loss of heterozygosity on chromosome 5q. For patients with disease confined to the site of origin, a 82-100% 5-year survival has been noted for endometrioid cell type; disseminated intraperitoneal disease, however, has a very poor associated prognosis, with a 0-12% 5-year survival overall.

Women with endometriosis-associated cancers most likely represent a different class of patients than traditional ovarian cancer patients and may require different therapeutic options.