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Simple ovarian cysts on ultrasound can be considered normal findings and safely ignored, while complex cysts are strongly associated with an increased cancer risk, a nested case-control study found.

Within 3 years, only a single case of ovarian cancer was diagnosed in over 15,000 women with simple ovarian cysts, for likelihood ratios of 0.00 for those under age 50 (95% CI 0.00-1.03) and 0.06 for those 50 and above (95% CI 0.01-0.48), according to Rebecca Smith-Bindman, MD, of the University of California San Francisco, and colleagues.

These ratios were not significantly different than those for women who had normal ovaries on ultrasound: 0.36 (0.18-0.71) and 0.36 (0.25-0.53), respectively, as reported in .

But across the two age groups (<50 and ≥50), the appearance of a complex cyst, a complex cyst with ascites, or a solid mass yielded an increased likelihood of cancer 8 to 74 times that of women with normal ovaries:

• Complex cyst: 8.20 (95% CI 4.21-15.90) and 7.60 (95% CI 5.00-11.59), respectively
• With ascites: 8.34 (95% CI 2.94-23.66) and 74.17 (95% CI 15.80-349.12)
• Solid mass: 8.08 (95% CI 1.86-36.12) and 10.08 (95% CI 3.25-31.21)

With the increased use of ultrasonography, and improved image quality, simple cysts are more frequently found.

"The result has been tissue sampling and surgery when little value comes from this assessment," the authors wrote. "Simple cysts are frequently encountered incidental and normal findings on pelvic imaging, and additional evaluation of these findings is not warranted."

In a published with the study, Deborah Levine, MD, of Beth Israel Deaconess Medical Center in Boston, agreed, writing that although it is known that simple cysts are almost always benign, there is a hesitancy to ignore them on ultrasound, especially if they are large or when they are seen in postmenopausal women.

Therefore, the study -- although not without limitations (inability to account for patient symptoms, only two-thirds of all pelvic ultrasounds were included in the analysis, inconsistent patient follow-up, among others) -- advances clinical knowledge, and adds "to the growing literature that asymptomatic simple cysts may be safely ignored, regardless of size and regardless of patient age," said Levine.

However, she noted that the quality of the ultrasonographic image will be key for a confident diagnosis of a simple versus complex cyst.

"With confident diagnosis of simple cysts, clinicians can be reassured that the likelihood of cancer is similar to that of patients without cysts, and management can be based on patient symptoms rather than on a benign incidental pelvic ultrasonographic finding," Levine wrote.

The nested case-control study included 72,093 women enrolled in Kaiser Permanente Washington who underwent pelvic ultrasonography between 1997 and 2008. The characteristics of ovarian masses discovered in 1,043 women were measured, and the researchers estimated frequencies for the entire cohort.

Of those, 210 women were diagnosed with ovarian cancer: 49 in those younger than age 50 and 161 in those 50 or older. Diagnosed subtypes included papillary serous cystadenocarcinoma (36.6%), endometrioid carcinoma (12.0%), serous cystadenocarcinoma (10.6%), and clear cell adenocarcinoma (8.5%).

Most examined women had normal ovaries (n=41,692). Simple cysts were the next most common finding, occurring in about one-quarter of women younger than 50 and about 13% of women 50 or older.

Among the women diagnosed with ovarian cancer, the most common ultrasound finding was a complex cyst, occurring in 63.3% of those younger than 50 and 55.9% of those 50 or older.