Study uncovers types of ovarian cancer linked to endometriosis
The link between endometriosis and a slightly increased risk of ovarian cancer has been confirmed in a US study.
The study, published in the Lancet Oncology, is the first to show which types of ovarian cancer are linked to the condition, which affects the womb.
About one women in every 20 will develop endometriosis. But, commenting on the finding, UK experts pointed out that the number of women with the condition who would go on to develop ovarian cancer was small.
Dr Paul Pharoah, a Cancer Research UK-funded researcher at the University of Cambridge, said that about one woman in 50 in the general population will develop ovarian cancer - about 2 per cent.
He added that previous research has shown that this risk increases to around one in 40 (2.5 per cent) for women with endometriosis.
The new study was carried out by the Ovarian Cancer Association Consortium, led by Professor Celeste Leigh Pearce from the University of Southern California, Los Angeles.
It looked at the overall results of 13 previous studies, including data from more than 23,000 women, over 9,800 of whom had cancer.
Three types of ovarian cancer were slightly more common in women with endometriosis: clear cell, endometrioid, and low-grade serous ovarian cancer.
But the most common form of the disease - high-grade serous ovarian cancer - and other less-common types were not linked with the condition.
In endometriosis, the lining of the womb (the endometrium) begins to grow on the outside of the womb and on the nearby organs.
It can be painful and sometimes affect a woman's fertility. It is usually treated with surgery or hormone therapy.
Lead author Prof Pearce said the research could lead to better prevention and early detection approaches, such as risk-reducing surgery and screening.
But Dr Pharoah said that the research had limited immediate relevance for women or their doctors: "While these finding are of some biological interest they have limited immediate clinical implications, as the increase in risk to women with endometriosis is small.
"The only well-established intervention to reduce ovarian cancer risk is surgical removal of the ovaries, and this would only be offered to women at much higher risks," he said.
He also pointed out that, in absolute terms, it showed lifetime risk of developing clear cell cancer - about 1 in 500, or 0.2 per cent - increased to 1 in 180 (or 0.55 per cent) for women with endometriosis.
"The lifetime risk of both endometriod and low-grade serous ovarian cancer are each about 1 in 400 and these also increases to 1 in 180 in women with endometriosis," he added - an increase from 0.25 per cent to 0.55 per cent.
Dr Emily Power, health information manager at Cancer Research UK, said that women should be aware of the disease's symptoms.
"Ovarian cancer can be difficult to detect at an early stage, so identifying women who are at higher risk could help doctors to develop more targeted monitoring in the future," she said.
"All women should be aware of the signs of ovarian cancer, like pain in the lower tummy, bloating, increased tummy size, difficulty eating or feeling full."