Risk of Malignant Ovarian Cancer Based on Ultrasonography Findings in a Large Unselected Population.

Importance: The risk of malignant ovarian cancer associated with simple cysts is unknown. Objective: To quantify the risk of ovarian cancer based on ultrasonographic characteristics of ovarian masses, including simple cysts, in a large unselected population. Design, Setting, and Participants: This was a nested case-control study of patients enrolled in Kaiser Permanente Washington, a large integrated health care system in Washington State. Participants were 72 093 women who underwent pelvic ultrasonography between January 1, 1997, and December 31, 2008. Analysis was completed in April 2017. Exposures: Ultrasonographic characteristics of ovarian masses measured in 1043 women, and also, using weights derived from the sampling strategy, estimated frequencies for the entire cohort. Main Outcomes and Measures: Malignant ovarian cancer, identified through December 31, 2011, by cancer registry linkage. Results: Among 210 women who were diagnosed as having ovarian cancer, 49 were younger than 50 years, and 161 were 50 years or older. Ultrasonography findings were predictive of cancer (C statistic, 0.89). The risk of cancer was significantly elevated in women with complex cysts or solid masses, with likelihood ratios relative to women with normal ovaries ranging from 8 to 74 and the 3-year risk of cancer ranging from 9 to 430 cases per 1000 women based on patient age and ultrasonography findings. In contrast, the 23.8% of women younger than 50 years and the 13.4% of women 50 years or older with simple cysts were not at a significantly increased risk of ovarian cancer compared with women with normal ovaries. Likelihood ratios associated with the detection of a simple cyst were 0.00 in women younger than 50 years (no cancers were identified) and 0.10 (95% CI, 0.01-0.48) in women 50 years or older, and the absolute 3-year risk of cancer ranged from 0 to 0.5 cases per 1000 women. Conclusions and Relevance: According to this study, the ultrasonographic appearance of ovarian masses is strongly associated with a woman's risk of ovarian cancer. Simple cysts are not associated with an increased risk of ovarian cancer, whereas complex cysts or solid masses are associated with a significantly increased risk of ovarian cancer.