Primary ovarian cancer after colorectal cancer: a Dutch nationwide population-based study

Background and purpose Women with colorectal cancer (CRC) are at risk not only of developing ovarian metastases, but also of developing a primary ovarian malignancy. Several earlier studies have in fact shown a link between the development of primary ovarian cancer and CRC. The purpose of this study was therefore to determine the risk of developing a primary ovarian cancer in women with prior CRC compared to the general population. Methods Data from the Netherlands Cancer Registry were used. All women diagnosed with invasive CRC between 1989 and 2017 were included. Standardized incidence ratios (SIRs) and absolute excess risks (AERs) per 10,000 person-years were calculated. Results During the study period, 410 (0.3%) CRC patients were diagnosed with primary ovarian cancer. Women with CRC had a 20% increased risk of developing ovarian cancer compared to the general population (SIR = 1.2, 95% CI: 1.1-1.3). The AER of ovarian cancer was 0.9 per 10,000 person-years. The risk was especially increased within the first year of a CRC diagnosis (SIR = 3.3, 95% CI: 2.8-3.8) and in women aged <= 55 years (SIR = 2.0, 95% CI: 1.6-2.6). Conclusion This study found a slightly increased risk of primary ovarian cancer in women diagnosed with CRC compared to the general population. However, this may be partly attributable to surveillance or detection bias. Nevertheless, our findings could be helpful for patient counseling, as CRC patients do not currently receive information concerning the increased risk of ovarian cancer.