Positive Predictive Value for Colorectal Lesions at CT Colonography: Analysis of Factors Impacting Results in a Large Screening Cohort

Leesburg, VA, July 1, 2019—Using optical colonoscopy as their reference standard for concordance, a trio of researchers from the United States and Italy demonstrated high positive predictive value for colorectal cancer screening using CT colonography (CTC), resulting in greater specificity and risk stratification for appropriate patient triage compared with other non-invasive screening tests.

In an American Journal of Roentgenology online exclusive Focus On study, University of Wisconsin School of Medicine and Public Health radiologist, Perry J. Pickhardt, MD, evaluated the positive predictive value for detecting colorectal lesions using only CTC compared to common stool-based assessments like the fecal occult blood test, fecal immunochemical test, and stool DNA. 

Of the 877 men and 773 women (median age 59.7 years) with 2688 total CTC-detected lesions 6 mm or larger, the overall positive predictive values were 88.8% by polyp and 90.8% by patient. 

In addition, a positive CTC examination pointed to the likelihood of abnormal tissue growth, as per-patient positive predictive values were 72.3% (1193/1650) for any neoplasia 6 mm or larger and 38.8% (641/1650) for advanced neoplasia. 

Perhaps more importantly, as Aunt Minnie reported, “CTC enabled radiologists to identify critical information about the kind of condition behind each positive finding.” 

For example, only 5.8% of positive CTC studies at the CTC Reporting and Data System (C-RADS) C2 category will have advanced neoplasia at optical colonoscopy; however, this increases to 67.1% and 79.4% for the C3 and C4 categories, respectively. 

“Similarly,” wrote Pickhardt, “although none of the 781 patients whose CTC studies were positive at the C-RADS C2 category (the lowest level of positive) had cancer, the cancer rate increases to over 50% at the C4 category (the most concerning positive level). By comparison, there is generally no such weighted information available to physicians and patients for a positive stool-based test.”

Founded in 1900, the American Roentgen Ray Society (ARRS) is the first and oldest radiology society in the North America, dedicated to the advancement of medicine through the profession of radiology and its allied sciences. An international forum for progress since the discovery of the x-ray, ARRS maintains its mission of improving health through a community committed to advancing knowledge and skills with an annual scientific meeting, monthly publication of the peer-reviewed American Journal of Roentgenology (AJR), quarterly issues of InPractice magazine, topical symposia and AJR Live Webinars, print and online educational materials, as well as awarding scholarships via The Roentgen Fund®.