Endometriosis and two similar conditions — leiomyomas and adenomyosis — tend to be found in people with endometrial cancer, suggesting a need to better understand how the three affect cancer risk and outcomes, a study says.
The study, “Co-existence of leiomyomas, adenomyosis and endometriosis in women with endometrial cancer,” was published in the journal Scientific Reports.
While in endometriosis the cells that line the inside of the uterus (endometrial cells) start growing elsewhere in the body, adenomyosis is a condition in which these endometrial cells grow into the muscle of the uterus itself. Leiomyomas, also called uterine fibroids, are non-cancerous growths of uterine tissue.
While some evidence suggests these conditions may be linked to an increased risk of endometrial cancer, findings are still inconclusive. In addition, most studies have only focused on assessing the individual contribution of each of these conditions, even though many of them can be found in the same person.
To explore their collective contribution to endometrial cancer risk, researchers in Australia evaluated the frequency of these three uterine conditions in people with endometrial cancer using data from the Australian National Endometrial Cancer Study (ANECS).
Among the 1,399 individuals whose data was analyzed, 817 had leiomyomas (58.4% of these cancer patients), 179 had endometriosis (12.8%), and 572 had adenomyosis (41%). In total, 1,568 instances of these conditions were found.
Researchers then conducted a statistical analysis to compare the observed frequencies of these conditions co-occurring, to what would be expected if the conditions were unrelated and only occurred at the rate seen in the general population. They found that the observed frequencies were significantly different from what would be expected.
In particular, they found significantly higher proportions of the population had none of these conditions (25.2% versus 21.4%), or had all three (5.0% versus 3.1%).
Put another way, individuals with adenomyosis were more likely to have endometriosis (15.6% versus 10.9%), as were those with leiomyomas (15.1% versus 9.8%), compared to those who did not. This suggests that the three conditions are related to each other, with the presence of one increasing the likelihood of the others.
Further analyses tested if any of these three conditions were significantly associated with various clinical and demographic factors.
Adenomyosis was found to be more common among women who reported taking oral contraceptives (73.9% versus 62.9%), and among those who had two or more full-term pregnancies (79% versus 68%).
Endometriosis was associated with a significantly younger age at which endometrial cancer was diagnosed (57 versus 62 years).
Researchers also noted a somewhat lower proportion of lower tumor grade (grades 1 and 2) among people with none of these conditions (68.5%), compared to those who had at least one (73.6% versus 89.5%). However, “sample sizes for some subgroups are too small to provide reliable estimates,” they wrote, meaning no definitive conclusions can be drawn from these observations.
Thirty people in the study were diagnosed with ovarian cancer in addition to endometrial cancer. Compared to the rest of the population, a significantly higher proportion of these individuals had endometriosis (12.1% versus 43.3%); the other two conditions did not differ significantly based on ovarian cancer status.
Finally, investigators looked for possible associations between the three uterine conditions and survival. They found a slight, but significant, association between the presence of leiomyomas and better overall and cancer-specific survival (reduced risk of just over 30% for both).
“Our case-only study was not able to directly estimate EC [endometrial cancer] risk associated with leiomyomas, adenomyosis and endometriosis,” the researchers wrote. They stressed that doing this kind of estimation would probably require samples of uterine tissue from individuals with no symptoms of disease, and these people would be unlikely to have a biopsy in the first place.
“Nevertheless,” they added, “our findings provide justification for further consideration of these three conditions in the aetiology [origin] of EC [endometrial cancer]. … Our recommendation is that all three conditions should be investigated more thoroughly as independent risk factors for EC in an appropriately designed study.”