Endometriosis is a benign disease in which uterine tissue grows outside the uterus in the form of small implants in the pelvis or peritoneum. These implants can be infiltrative (deep) or superficial. It has previously been shown that endometriosis can increase the risk of ovarian cancer.  

An article published this week in the journal JAMA includes data from nearly 500,000 people in the US state of Utah, comparing women who had endometriosis with those who had never had it and followed up to see how many developed ovarian cancer. The results of this analysis are novel because of the large sample size of people included and because it analyses by different subtypes of ovarian cancer. 

The main conclusions are that endometriosis is confirmed to increase the risk of virtually all subtypes of ovarian cancer, but especially significantly increases the risk of cancer of the following types: clear cell, low-grade serous, carcinosarcoma and endometrioid ovarian cancer. In these subtypes, people who have had endometriosis are 7 to 11 times more likely to develop them than the normal population. Furthermore, if we restrict ourselves to patients with infiltrating endometriomas, excluding those with superficial endometriosis, the risk of developing any of the above subtypes of ovarian cancer is particularly high.  

On the other hand, the study shows that the increased risk of cancer is observed up to 20 years after the diagnosis of endometriosis. This has led the authors to conclude that given the relevant increased risk in these patients, early diagnostic measures could be proposed in this population. Studies of early diagnosis in ovarian cancer have not shown it to be a cost-effective measure, most likely because the proportion of ovarian tumours is fortunately very low in the general population. However, it makes sense to consider screening specifically for this higher risk population.