Ovarian cancer risk was higher in women with endometriosis overall and markedly increased in those with severe forms, a large population-based cohort study found.
The findings, published in JAMA, suggest these women may benefit from counseling on ovarian cancer risk and prevention and potentially from targeted screening, according to a group led by Mollie E. Barnard, ScD, of the Huntsman Cancer Institute at the University of Utah in Salt Lake City.
While the absolute increase in number of cases was small, endometriosis patients overall had a more than fourfold higher risk for any type of ovarian cancer. Those with more severe forms, such as ovarian endometriomas or deep infiltrating endometriosis, had a nearly 10-fold higher risk of any type of ovarian cancer. In addition, those with more severe endometriosis had a 19-fold higher risk of type 1 (slow-growing) ovarian cancer and almost three times the risk of the more aggressive type 2.
“Given the rarity of ovarian cancer, the excess risk was relatively small, with 10-20 additional cases per 10,000 women. Nevertheless, women with endometriosis, notably the more severe subtypes, may be an important population for targeted cancer screening and prevention studies,” said corresponding author Karen C. Schliep, PhD, MSPH, associate professor in the university’s Division of Public Health.
Prior studies have shown modest associations between endometriosis and ovarian cancer, Dr. Schliep said in an interview. A 2021 systematic review and meta-analysis found endometriosis conferred nearly double the risk of ovarian cancer, although associations varied by ovarian cancer histotype. Few studies have been large enough to assess associations between endometriosis types — including superficial or peritoneal endometriosis vs ovarian endometriomas or deep infiltrating endometriosis and ovarian cancer histotypes such as low-grade serous, endometrioid, clear cell, and mucinous carcinomas (type 1), and the most aggressive and lethal form, high-grade serous type 2, she said in an interview. “Our large health administrative database of over 11 million individuals with linked electronic health and cancer registry data allowed us to answer this as yet poorly studied research question.”
Study Details
Drawing on Utah electronic health records from 1992 to 2019, the investigators matched 78,893 women with endometriosis in a 1:5 ratio to unaffected women. Cases were categorized as superficial endometriosis, ovarian endometriomas, deep infiltrating endometriosis, or other, and the types of endometriosis were matched to ovarian cancer histotypes.
The mean age of patients at first endometriosis diagnosis was 36 and the mean follow-up was 12 years. Compared with controls, endometriosis patients were more likely to be nulliparous (31% vs 24%) and to have had a hysterectomy (39% vs 6%) during follow-up.
There were 596 reported cases of ovarian cancer in the cohort. Those with incident endometriosis were 4.2 times more likely to develop ovarian cancer (95% CI, 3.59-4.91), 7.48 times more likely to develop type 1 ovarian cancer (95% CI, 5.80-9.65), and 2.70 times more likely to develop type 2 ovarian cancer (95% CI, 2.09-3.49) compared with those without endometriosis.
The magnitudes of these associations varied by endometriosis subtype. Individuals diagnosed with deep infiltrating endometriosis and/or ovarian endometriomas had 9.66 times the risk of ovarian cancer vs individuals without endometriosis (95% CI, 7.77-12.00). “Women with, compared to without, more severe endometriosis had a 19-fold higher risk of type 1 ovarian cancer, including endometrioid, clear cell, mucinous, and low-grade serous,” Dr. Schliep said, with associated risk highest for malignant subtypes such as clear cell and endometrioid carcinoma (adjusted hazard ratios, 11.15 and 7.96, respectively.
According to Dr. Schliep, physicians should encourage endometriosis patients to be aware of but not worry about ovarian cancer risk because the likelihood of developing it remains low. For their part, patients can reduce their risk of cancer through a balanced diet with low intake of alcohol, regular exercise, a healthy weight, and abstention from smoking.
Her message for researchers is as follows: “We need more studies that explore how different types of endometriosis impact different types of ovarian cancer risk. These studies will guide improved ovarian cancer screening and prevention strategies among women with severe endometriosis, with or without other important ovarian cancer risk factors such as BRCA 1/2 variations.”
An accompanying editorial called the Utah study “eloquent” and noted its distinguishing contribution of observing associations between subtypes of endometriosis with overall risk for ovarian cancer as well as histologic subtypes of epithelial ovarian cancer.
Nevertheless, Michael T. McHale, MD, of the Department of Obstetrics, Gynecology, and Reproductive Sciences at Moores Cancer Center, UC San Diego Health, University of California, expressed some methodological concerns. Although the authors attempted to control for key confounders, he noted, the dataset could not provide details on the medical management of endometriosis, such as oral contraceptives or gonadotropin-releasing hormone agonists. “Additionally, there is a possibility that women in the control cohort could have had undiagnosed endometriosis,” he wrote.
Furthermore, making clinical recommendations from these reported observations, particularly with respect to deep infiltrating endometriosis, would require a clear and consistent definition of this type in the dataset over the entire study interval from 1992 to 2019 and for the state of Utah, which the authors did not provide.
“Despite this potential challenge, the increased risk associated with deep infiltrating and/or ovarian endometriosis was clearly significant,” Dr. McHale wrote.
And although the absolute number of ovarian cancers is limited, in his view, the increased risk is sufficiently significant to advise women who have completed childbearing or have alternative fertility options to consider “more definitive surgery.”
This study was supported by multiple not-for-profit agencies, including the National Cancer Institute, the University of Utah, the National Center for Research Resources, the Utah Department of Health and Human Services, the Utah Cancer Registry, the US Centers for Disease Control and Prevention, the Huntsman Cancer Foundation, the National Institutes of Health, and Doris Duke Foundation. Dr. Barnard reported grants from the National Cancer Institute during the conduct of the study and personal fees from Epi Excellence LLC outside the submitted work. Other coauthors reported similar funding from nonprofit agencies or private research organizations. Dr Schliep disclosed no competing interests. Dr McHale reported educational consulting for Eisai Training outside the submitted work.