This group of 4331 surveyed Endometriosis Association members who reported surgically diagnosed endometriosis commonly reported other physician-diagnosed diseases. Of the infectious diseases, recurrent upper respiratory infections and recurrent vaginitis were more likely in the study population, but candidiasis and mononucleosis were not. The nature of these infections (bacterial, viral, fungal) is not known, and thus many women with recurrent vaginitis may have had vaginal candidiasis and therefore were unsure of the diagnosis. Melanoma and ovarian cancers were reported by about 30 and 10 women, respectively, but were more common in the study population than in similarly aged women in the general population. Addison’s disease and Cushing’s syndrome were rare but were more common in the survey respondents than in the general population. However, their low absolute numbers did not assure statistical significance. Mitral valve prolapse was common.
Studies have noted an increased risk of ovarian cancer with endometriosis, especially among patients with a long-standing history (>10 years) of the disease and diagnosis before age 30 (4
). Melin et al. reported that those with ovarian cancer diagnosed after endometriosis had had cancer at a younger age when compared with the general population (5
Molecular investigations on the transformation of endometriosis to ovarian cancer have attributed it to various genetic mutations (17
). The androgenic agent, danazol, which is commonly used in treating endometriosis, has been shown to be an independent risk factor for ovarian cancer, with women who have ever used danazol having a 3.2 times increased risk of ovarian cancer compared with those who did not (22
). We have noted that danazol use was common in this cohort of women (23
). The potential role of endogenous or exogenous hormones in promoting the development of ovarian cancer continues to be explored.
Melanoma has been reported in those with subfertility, with an increased relative risk of melanoma among women with primary infertility due to endometriosis (12
). An increased incidence of dysplastic nevi, a precursor lesion of melanoma, has been documented in patients with endometriosis (24
While our study suggests an increased occurrence of ovarian cancer and melanoma, the low prevalence of ovarian cancer may be explained by the young age of the study population. While the relatively low prevalence of both and, in sensitivity analysis, the disappearance of increased ovarian cancer prevalence with moderate misclassification brings into question these findings, there are some characteristics of this population that may be responsible for this lower prevalence. The common treatments of oral contraceptives and other hormones for endometriosis, which are frequently used in this population (23
), may have lowered the risk of ovarian cancer. In addition, half of the women reported oophorectomy and/or hysterectomy (20% oophorectomy, 18% hysterectomy, and 12% both) (23
), possibly reducing the risk of ovarian cancer in these women who reported surgically diagnosed endometriosis.
The lack of an increased prevalence of breast cancer in the study population may have been decreased by the high rate of oophorectomy (32%), which might offset the effect of the high rate of infertility (1
) and hormone use (23
). The lower prevalence may be expected in this younger population as incidence increases with age, with the highest rates in women over age 50. We do not know whether the members of this cohort would have developed breast cancer as they aged. Other studies assessing the relation between endometriosis and breast cancer have been inconclusive or have shown no relationship (4
The higher prevalence of recurrent upper respiratory and vaginal infections might be expected as other autoimmune diseases have been reported by this group of women and immune abnormalities occur in women with endometriosis (1
). Due to the self-reported nature of the data, it is possible that women mistakenly reported any recurrent or chronic vaginal complaint as vaginitis. Similarly, recurrent upper respiratory infections might indicate other recurrent respiratory problems like sinusitis or frequent colds. Nonetheless, physician-diagnosed recurrent upper respiratory or vaginal infections are likely in this group of women because, by sensitivity analyses, high degrees of misclassification would need to exist for these observed differences to disappear.
The lower prevalence of candidiasis may be due to its narrow definition as “allergy and systemic infection with the yeast Candida albicans,” a condition hypothesized to be common in women with endometriosis, that was used in the survey. The prevalence of women with mononucleosis may have been underreported because women may not have been familiar with the term “mononucleosis” or may have had the disease but not been diagnosed by a physician.
The prevalence of Cushing’s syndrome and Addison’s disease were extremely low, suggesting that their statistical significance occurred by chance.
The higher prevalence of mitral valve prolapse is negated with minimal misclassification. Perhaps women were diagnosed with mitral valve prolapse during evaluation for surgery, although whether diagnosis was made by echocardiogram was not ascertained.
While this study primarily involved white, young, educated, and more affluent women, the large sample size strengthened the study and provided statistical power. In addition, the survey collected information regarding diagnoses, including age and treatment, which were used to corroborate responses. The sensitivity analysis helped assess the validity of the findings.
There are, however, several limitations. First, conditions are self-reported, and it is not possible to confirm the diagnosis by laboratory tests or review of medical records. Although the analysis was restricted to women reporting a surgical diagnosis of endometriosis, disease misclassification for endometriosis was possible. Misclassification of other conditions may have occurred, leading to an overestimate of the true prevalence in the study sample or an underestimate in the general population. Selection bias may also exist, since the 47% of women who opted to complete the questionnaire may be different from nonrespondents or other members of the Endometriosis Association; in addition, they were more educated than the general population. It would be ideal to compare results from women with endometriosis with a similar group of women without endometriosis completing the same survey, but it might be difficult to administer to women without endometriosis since the survey was specifically designed to capture the health experiences of women with endometriosis.
Our study has many strengths, and careful methodological steps were taken to minimize the likelihood of errors and biases. While the limitations are less likely to affect the study’s internal validity, the study findings can be generalized only to women with endometriosis similar to those who belong to the Endometriosis Association. In addition, women who join support groups may not be representative of the population of individuals with the disease.
In conclusion, our study describes the prevalence of several coexisting diseases suspected to be common in women with endometriosis. Respondents to the Endometriosis Association survey were more likely to have recurrent upper respiratory and vaginal infections than the general population. As others have reported, ovarian cancer and melanoma were statistically more common in the study population than in the general population. The younger age of the study population and the low prevalence limit our ability to make inferences about these associations. These findings support our previous observation that women in this study reporting pain and surgically diagnosed endometriosis also report a high prevalence of autoimmune diseases. This documents another potential association with the immune system, which may help focus future research into this disease.