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Risk of Gynecologic Cancer According to the Type of Endometriosis

Saavalainen, Liisu, MD; Lassus, Heini, MD, PhD; But, Anna, MSc; Tiitinen, Aila, MD, PhD; Härkki, Päivi, MD, PhD; Gissler, Mika, PhD; Pukkala, Eero, PhD; Heikinheimo, Oskari, MD, PhD

doi: 10.1097/AOG.0000000000002624
Contents: Gynecologic Oncology: Original Research

OBJECTIVE: To assess the risks of gynecologic cancer according to the type of endometriosis in women with surgically verified endometriosis.

METHODS: This is a population-based study of women with surgically verified endometriosis retrieved from the Finnish Hospital Discharge Register 1987–2012 (N=49,933); the subtypes of ovarian (n=23,210), peritoneal (n=20,187), and deep infiltrating (n=2,372) endometriosis were analyzed separately. Gynecologic cancers were obtained from the Finnish Cancer Registry. The outcome measure was the standardized incidence ratio (95% CI) calculated as the ratio between the observed to the expected number of cancers and defined for each gynecologic cancer and further stratified according to the histology, follow-up time since surgery, and age at follow-up. The follow-up was 838,685 person-years, and the Finnish female population served as the reference.

RESULTS: Endometriosis was associated with increased risk of ovarian cancer (standardized incidence ratio 1.76 [95% CI 1.47–2.08]), especially with endometrioid (3.12 [2.15–4.38]) and clear cell (5.17 [3.20–7.89]) histologic type and to a lesser extent with serous type (1.37 [1.02–1.80]). The risk of ovarian cancer was highest among women with ovarian endometriosis and especially for endometrioid (4.72 [2.75–7.56]) and clear cell (10.1 [5.50–16.9]) ovarian cancer, occurring 5–10 years after the index surgery. The overall risk of ovarian cancer was not increased among women with peritoneal and deep infiltrating endometriosis. However, peritoneal endometriosis was associated with a twofold increase in risk of endometrioid histology. The risk of endometrial cancer was not altered in the entire cohort. The standardized incidence ratio for precancerous cervical lesions was 0.81 (0.71–0.92) and for invasive squamous cell carcinoma of the cervical cancer 0.46 (0.20–0.91).

CONCLUSION: The excess risk of ovarian cancer among women with ovarian endometriosis translates into two excess cases per 1,000 patients followed for 10 years. Acknowledging these risks is important when planning long-term management of women with endometriosis.

Ovarian endometriosis is associated with an increased risk of ovarian cancer, resulting in two excess cases per 1,000 surgically verified patients during 10 years of follow-up.

Departments of Obstetrics and Gynecology and Public Health, University of Helsinki and Helsinki University Hospital, Helsinki, and the National Institute for Health and Welfare, Helsinki, Finland; the Department of Neurobiology, Care Sciences and Society, Division of Family Medicine, Karolinska Institute, Stockholm, Sweden; and the Finnish Cancer Registry, Helsinki, and the Faculty of Health Sciences, University of Tampere, Tampere, Finland.

Corresponding author: Oskari Heikinheimo, MD, PhD, Department of Obstetrics and Gynecology, Helsinki University Hospital, PO Box 140, FI-00029 HUS Helsinki, Finland; email:

The research funds of the Hospital District of Helsinki and Uusimaa supporting this study are gratefully acknowledged.

Financial Disclosure The authors did not report any potential conflicts of interest.

Presented in part at the 13th World Congress on Endometriosis, May 17–20, 2017, Vancouver, British Columbia, Canada.

The data were obtained from the Finnish Hospital Discharge Register, the Finnish Cancer Registry, and the Finnish Population Register Center.

Each author has indicated that he or she has met the journal's requirements for authorship.

© 2018 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.