Risk of Ovarian Cancer: Algorithm Determines Step 2
Dr. Lu described the 2-step strategy for Decoded Science, “ROCA looks at CA-125 over time and determines whether a woman is (1) safe to return in 1 year for a repeat CA-125; (2) should come back in 3 months for another CA-125 to evaluate the trend; or (3) needs to go for a transvaginal ultrasound and see their physician.”
The purpose of this study was to measure the specificity and PPV of the 2-step screening strategy. These are common statistical measures of the performance of a test.
Specificity refers to the probability of correctly identifying individuals with no disease. The PPV is the probability that in case of a positive test, that the individual really has the specified disease.
In principle, a specificity of 97% and PPV of 10% would be a respected balance of risk versus benefit. This means that for every 10 operations performed, doctors would confirm one ovarian cancer case.
After 11 years of follow-up, researchers reported that the ROCA determined 83.4% of participants remained in the low-risk category (ROCA score was less than 1 in 2,000); 13.7% fell into the intermediate-risk group (ROCA score between 1 in 2,000 and 1 in 500); and 2.9% were in the high risk group (ROCA score greater than 1 in 500). There were seven confirmed cases, four with low-grade invasive ovarian cancer. Exceeding estimated values, specificity was calculated at 99.6% and PPV at 40%, which means that doctors found approximately one invasive ovarian cancer case out of every 2 to 3 operations – a very high detection rate.
Ovarian Cancer Research to Clinical Settings
When asked if there were any surprising results, Dr. Lu explains, “CA-125 is not a new marker. I was surprised at how taking an old marker and applying it in a new way would be so effective.”
While there was enough power to test the effectiveness of this strategy on early detection, authors state that the findings from this study are “not practice-changing at this time.” Dr. Lu explains, “We need to wait for the U.K. study to determine if this strategy decreases deaths from ovarian cancer, which is the gold standard for any screening test. Those results should be available in 2015.”
She also mentions the substantial sample size needed to detect the sensitivity (number of true positives) of the strategy, “The U.K. study has 50,000 women getting screened similar to our strategy with ROCA, and 100,000 control women not getting screened.”
Recommending Routine Checks After Further Testing
If the U.K. study does indeed show decreased deaths from ovarian cancer, Dr. Lu would recommend a routine screening, “We would do it in all postmenopausal women over 50 at their annual visit with their gynecologist or family physician.”
Lu KH, Skates S, Hernandez MA, et al. A 2-stage ovarian cancer screening strategy using the Risk of Ovarian Cancer Algorithm (ROCA) identifies early-stage incident cancers and demonstrates high positive predictive value. (2013). Cancer. Accessed August 27, 2013.
Howlader N, Noone AM, Krapcho M, Garshell J, Neyman N, Altekruse SF, Kosary CL, Yu M, Ruhl J, Tatalovich Z, Cho H, Mariotto A, Lewis DR, Chen HS, Feuer EJ, Cronin KA (eds). SEER Cancer Statistics Review, 1975-2010. (2013). National Cancer Institute. Accessed August 27, 2013.
American Cancer Society. Learn about Cancer. Ovarian Cancer: Early Detection, Diagnosis, and Staging Topics. (2013). Accessed August 27, 2013.
Mayo Clinic. CA 125 test. (2011). Tests and Procedures. Accessed August 27, 2013.