Researchers find odds of having ovarian cancer up to 2.6 times higher for women carrying genetic risk factors for endometriosis. These women also have a higher risk of developing certain ovarian cancers. A study of genetic markers in nearly 15,000 women with endometriosis and more than 25,000 women with ovarian cancer has found what researchers say is a causal link between the two conditions.

“We have estimated that the odds of having ovarian cancer over a lifetime is up to 2.6 times higher for women carrying genetic risk factors for endometriosis,” said the study’s lead author, Dr Sally Mortlock of the University of Queensland.

The genetic link was specific to certain kinds of epithelial ovarian cancer – the most common category, which accounts for an estimated 90% of cases.

Endometriosis – a condition in which the tissue similar to the lining of the uterus grows outside the uterus – affects an estimated one in 10 women of reproductive age.

“Endometriosis affects as many women as diabetes and asthma yet it has not received the same level of attention or funding, leaving women to suffer in silence,” Mortlock said. Mortlock emphasised that while there was a “significant overlap in genetic risk factors” between the two conditions, the overall risk for developing ovarian cancer was still low. She said having endometriosis increased the risk of developing ovarian cancer to one in 55, compared with an estimated ovarian cancer risk of one in 76 women generally.

“We explored specific areas of DNA that increase the risk of both diseases,” Mortlock said. The researchers found that women with 27 genetic markers – which have previously been strongly linked to endometriosis – were also more likely to have ovarian cancer. Using a statistical method known as Mendelian randomisation, the team were able to demonstrate a causal genetic link, and establish “directionality from endometriosis to EOC [epithelial ovarian cancer] risk rather than vice versa”.

“Some of these genes have important roles controlling the ability of our cells to adhere, or stick, to each other and respond to hormones,” Mortlock said. “This gives us clues that these pathways might be important in disease development and progression.” The identified genes could be used as future drug targets to treat both conditions, she said.

Tracy O’Mara, an associate professor at the QIMR Berghofer Medical Research Institute, who was not involved in the study, said the research demonstrated a causal relationship between the two conditions, which have previously been linked in epidemiological studies. “The relationship between endometriosis and ovarian cancer has [previously] been looked at observationally,” O’Mara said. “It’s nice that they’ve used these genetic techniques … it really shows the shared biology between the two.”

One limitation of the study is that its DNA data only included women of European ancestry. “Whether the results can be extrapolated to other ethnic groups is something that would need to be looked at as well,” O’Mara said. The research was published in the journal Cell Reports Medicine.