A large study based on the Nurses’ Health Study II (NHSII) confirms that endometriosis is associated with increased risk of ovarian cancer. Moreover, it further clarifies that this condition is not linked to a greater risk for endometrial cancer.
The study, “Endometriosis and risk of ovarian and endometrial cancers in a large prospective cohort of U.S. nurses,” was published in the journal Cancer Causes & Control.
Many women with endometriosis are asymptomatic and only in more severe cases are these patients subjected to minimally invasive surgery, or laparoscopic surgery, to confirm diagnosis. Because of this, many studies rely on self-reports of the condition and not on fully confirmed diagnoses, which may impact the results obtained.
To confirm previous reports of association between endometriosis and ovarian cancer, the authors of the NHSII study compared self-reported vs. laparoscopically confirmed cases of endometriosis, to the incidence of this type of cancer.
The authors also evaluated the association between endometriosis and the risk of endometrial cancer, which remains unclear because it has been explored scarcely.
Based on the NHSII, one of the largest studies to address risk factors for major chronic diseases in women, the authors obtained lifestyle, health behaviors, and medical history-related information from 116,429 female registered nurses.
The authors reported that throughout 18 years of follow-up, 228 cases of ovarian cancer and 166 cases of endometrial cancer were documented, representing 0.22% and 0.17% of the eligible women, respectively.
They found that self-reported cases of endometriosis were associated with an 81% increased risk of ovarian cancer, compared to women with no history of this condition. This association was even stronger in women who had endometriosis confirmed via laparoscopic surgery, with 114% increased risk to develop ovarian cancer.
Evaluation of the endometrial cancer cases showed that endometriosis, either self-reported or surgically confirmed, was not associated with increased risk for this type of cancer.
Delays in diagnosis or post-endometriosis diagnosis factors, such as oral contraceptive use and parity, had little impact in the risk assessments.
“This study adds to the evidence that endometriosis is not strongly linked to endometrial cancer risk and that the association with ovarian cancer is robust to misclassification, diagnostic delay, and changes in exposures post-endometriosis diagnosis,” the authors wrote.
This study suggests that, although self-reports of endometriosis may be confounding and lead to misclassification, they still are reliable determinants for ovarian cancer risk associations. However, the authors stressed that these results should be replicated in future studies.