Risk of nonovarian cancer in a nationwide‐based study of nearly 5000 women with borderline ovarian tumors in Denmark

Evidence regarding cancer risk after borderline ovarian tumors (BOTs) is limited. We conducted a nationwide cohort study examining the incidence of non-ovarian cancers in women with serous or mucinous BOTs compared to the general female population with up to 41 years of follow-up. Through the nationwide Pathology Registry, we identified nearly 5,000 women with BOTs (2,506 serous and 2,493 mucinous) in Denmark, 1978–2018. We computed standardized incidence ratios (SIRs) with 95% confidence intervals (CIs) as relative risk estimates of specific non-ovarian cancers. Compared to general female population rates, women with serous BOTs had increased rates of particularly malignant melanoma (SIR=1.9; 95% CI: 1.3–2.6), thyroid cancer (SIR=3.0; 95% CI: 1.4–5.4) and myeloid leukemia (SIR=3.2; 95% CI: 1.5–5.8), and women with mucinous BOTs had elevated rates of lung cancer (SIR=1.7; 95% CI: 1.3–2.1), pancreatic cancer (SIR=1.9; 95% CI: 1.2–2.9) and myeloid leukemia (SIR=2.3; 95% CI: 0.9–4.7). We found no convincing association with neither breast nor colorectal cancer in women with BOTs. This is the first large nationwide study showing that women with specific types of BOTs have increased risks of several non-ovarian cancers, likely due to some shared risk factors or genetic characteristics. This article is protected by copyright. All rights reserved.