Blood Test Shows Promise as Colorectal Cancer Screen

SAN DIEGO -- A blood test that evaluates natural killer cell activity (NKA) showed high sensitivity and, consequently, high negative predictive value in screening patients at risk for colorectal cancer that could make it clinically useful if confirmed in further studies, researchers said here.

The quantitative ELISA test for low NKA, called NKvue and offered by one clinical lab in the U.S. and several in Canada, showed sensitivity of 85.7% and a negative predictive value of 99.3% in a trial conducted among patients at increased risk for colorectal cancer on the basis of positive fecal immunochemical test (FIT) results or other factors, said Gilles Jobin, MD, of the University of Montreal.

Low NKA has been reported in colorectal cancer and several studies have linked it to cancer risk generally, Jobin explained.

At the Digestive Disease Week meeting, Jobin presented results in the first 762 evaluable patients in an ongoing study. These were individuals who underwent colonoscopy for definitive detection of colorectal cancer, as well as NKA testing, primarily because of risk factors for the disease. Most commonly these were personal or family history of colorectal cancer, rectal cancer, or positive FIT results.

Twenty-one of the 762 patients were found to have colorectal cancer at colonoscopy.

Using an NKA value of 200 pg/mL as the cutoff, the testing gave a positive result for 18 of the 21 patients with colorectal cancer, as well as in 173 participants who had no cancer or neoplasia of any kind. That translated to a specificity of 59.5% for colorectal cancer and 58.3% for large polyp (>10 mm) detection.

However, the 85.7% sensitivity for colorectal cancer led to 99%-plus negative predictive value, meaning that a negative result was highly accurate, Jobin said. He told MedPage Today that this would be the true clinical value of the test, if studies in a more representative screening population show similar results -- a negative result could spare patients from undergoing a colonoscopy under some circumstances.

He noted that, in Canada, the test costs about C$125, substantially lower than a colonoscopy. He also suggested that, as a blood test, it would be more acceptable to the many patients who delay or avoid colonoscopies because of their various burdens.

Replication of the current study's favorable results in broader populations far from certain, however.

The trial excluded patients with active bacterial and viral infections, those with autoimmune disorders or who had used immunosuppressive drugs within the past 6 months, and anyone with previous cancer treatments including surgery or chemotherapy, all of which may alter NKA values.

In an ordinary screening population, which would likely include people with undiagnosed infections or other cancers, the test could be less accurate, Jobin said. He said the next phase of evaluation should give a better idea of how accurate the test will be in a more realistic clinical setting.

The NKA test is currently available commercially in the U.S. as a lab-developed test performed by Cynvenio. It was originally developed by a Korean firm, ATGen.

The study had support from ATGen. Other potential conflicts of interest were not reported.

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Blood Test Shows Promise as Colorectal Cancer Screen