Diagnosis & Therapy

Endometriosis associated with modest increase in ovarian cancer risk

Endometriosis associated with modest increase in ovarian cancer risk

A 15-year national Finnish study looking at over 800,00 person years in women with endometriosis found that ovarian endometriosis more than doubled the relative risk for ovarian cancer, but that the absolute excess risk of ovarian cancer in the cohort was “quite small. Read our summary of the article and watch a video with Justin Chura, MD, a gynecologic oncologist who puts this new research in perspective.


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Perspectives on Endometriosis Management


Endometriosis appears to be associated with an increased risk of subsequent ovarian cancer, but the overall increase, which varies by histology type, is modest, according to the most recent study to evaluate this relationship.

Overall, the excess risk for ovarian cancer was increased by 1 case per 1,000 women with any form of endometriosis followed for 10 years and by 2 cases per 1,000 women in those with ovarian endometriosis, according to a population-based study that employed the Finnish Hospital Discharge Register. Risk varied by histology type.

Over a 15-year period from 1987 to 2012, data were collected on all surgically diagnosed cases of endometriosis in a national database. The gynecologic cancer incidence in the 49,933 endometriosis cases collected over this time period was compared with the Finnish female population on the basis of a standardized incidence ratio (SIR).

With 838,685 person-years of follow-up in the endometriosis population, the SIR for ovarian cancer was 1.76 (95% confidence interval, 1.47-2.08) overall. By histology, the SIR ranged from 1.37 for serous type (95% CI, 1.02-1.80) to 5.17 (95% CI, 3.20-7.89) for clear cell type. The SIR for the endometrioid histologic type fell in between at 3.12 (95% CI, 2.15-4.38), Liisu Saavalainen, MD, of the University of Helsinki and associates reported in Obstetrics & Gynecology.

When limited to those with ovarian endometriosis, risks climbed overall and for the specific histologic types. For example, the SIR for endometrioid histologic type climbed to 4.72 (95% CI, 2.75-7.56) while the SIR for the clear cell type climbed to 10.1 (95% CI, 5.50-16.9). Endometriosis of the peritoneal or deep infiltrating histologic type was not associated with an increased risk of ovarian cancer.

There was no association between endometriosis and other gynecologic cancers, including uterine, cervical, endometrial, vulvar, or vaginal cancers. Rather, endometriosis was associated with a protective effect for squamous cell cervical cancer, producing a SIR of 0.46 (95% CI, 0.20-0.91). The protective effect appeared to be even greater for peritoneal endometriosis (SIR 0.25; 95% CI, 0.03-0.90), the investigators said.

Although these data suggest that endometriosis doubles the risk of ovarian cancer (SIR of 1.76 for any endometriosis and 2.6 for ovarian endometriosis), Dr. Saavalainen and associates emphasized that these data suggest the absolute excess risk of ovarian cancer in the entire cohort is “quite small.”

A low background rate was responsible for magnifying the relative risk. Overall, the absolute increase in ovarian cancer associated with ovarian endometriosis was only 2 cases of ovarian cancer per 1,000 patients followed for 10 years. 

Endometriosis, which produces chronic inflammation and has other characteristics associated with an increased risk of neoplastic pathways, such as tissue invasion and reduced apoptosis, has long been suspected as an ovarian cancer risk factor. And these new data are consistent with previous case-control studies that produced relative risks ranging from 1.3 to 1.9, according to the investigations. Previous studies also have associated clear cell and endometrioid histologies with a greater relative overall risk of ovarian cancer.

The strength of this study was its reliance on a national database with nearly complete data on the Finnish population, according to the authors. Although this study required a surgical diagnosis of endometriosis for inclusion among cases, suggesting that cases of endometriosis with a low symptomatic burden were not included, 37% of the endometriosis cases ultimately included were identified during surgery performed for another reason.

The study was funded by the hospital district of Helsinki and Uusimaa. The authors reported no relevant financial disclosures.

SOURCE: Saavalainen L et al. Obstet Gynecol. 2018;131:1095-1102.