Associations between different cancer types are known. The affirmation of the risk for non-ovarian cancer after ovarian borderline tumors (BOT) is, however, sparse.
To analyze the risk of subsequent or simultaneous cancers in women with BOTs compared with the general female Swedish population.
An open cohort study (1995-2018) was conducted where a diagnosis of BOTs as well as subsequent or simultaneous cancer diagnoses were obtained from the Swedish Cancer Register and matched to the Total Population Register. Each woman with BOT was followed until non-ovarian cancer, death or emigration and could only be included once for the outcome. Standardized incidence ratios (SIRs) with 95% confidence intervals (CIs) for specific non-ovarian cancers were analyzed.
The 4998 women with serous and mucinous BOTs were diagnosed during 1995-2018 with a mean age of 55.7 years (SD 16.0) at diagnosis. Compared with the general female population, women with BOTs had increased risks for non-ovarian cancer in colon (SIR = 2.5; 95% CI 2.0-3.1), rectum (SIR = 1.7; 95% CI 1.1-2.5), small intestine (SIR = 5.0; 95% CI 2.3-9.5), cervix (SIR = 2.5; 95% CI 1.4-4.2), endometrium (SIR = 2.4; 95% CI 1.9-3.1), pancreas (SIR = 2.3; 95% CI 1.4-3.5), upper aerodigestive tract (SIR = 2.2; 95% CI 1.2-3.8), lung (SIR = 1.8; 95% CI 1.4-2.3), kidney (SIR = 2.3; 95% CI 1.4-3.7) and bladder (SIR = 1.8; 95% CI 1.1-2.8). Among women with serous BOTs, the risk of thyroid gland cancer (SIR = 3.1; 95% CI 1.2-6.4) was also increased. Lung and pancreas cancer showed increased risks more than 1 year after a diagnosis of BOT.
This Swedish population-based study demonstrated an increased risk of multiple malignancies including lung and pancreatic cancers beyond the first year of diagnosis in patients with borderline ovarian tumors (BOTs), suggesting a potential shared etiology.

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