A blood test for colon cancer

From practiceupdate.com

Italics are mine.
--------------------------------------------
January 20, 2018—San Francisco—A liquid biopsy that identifies circulating tumor cells (CTCs) in the bloodstream can detect colorectal cancer at an early stage, with accuracy ranging from 84 to 88%.

This finding of a large-scale evaluation of the test was reported at the 2018 Gastrointestinal Cancer Symposium, from January 18 – 20.

Wen-Sy Tsai, MD, of Linkou Chang Gung Memorial Hospital, Taipei, Taiwan, explained that most studies of CTCs have been able to detect late-stage colorectal cancer. The present evaluation is one of the first clinical studies to show that CTCs can be useful for detecting early-stage disease.

According to Dr. Tsai, these findings may present an option for patients who are hesitant to undergo a screening colonoscopy or are not comfortable returning stool-based test kits.

A total of 620 participants over age 20 years who presented for routine colonoscopy or had been diagnosed with confirmed colorectal cancer were enrolled. Based on colonoscopy and biopsy, 438 subjects were found to harbor either adenomatous polyps or early- to late-stage colorectal cancer. The remaining, comparison group exhibited no signs of precancerous growths or colorectal cancer.

From each of the 620 enrollees, 2 mL of blood was tested for CTC analysis through routine blood draw. Blood samples were processed using the CMx platform, an assay that captures rare CTCs such as those found in early-stage cancer on a lipid-coated chip that mimics human tissue. In blinded analysis, results of these assays were then compared with colonoscopy results.

In prior studies, this assay was found to detect very small numbers of CTCs, even at the level of one CTC per billion blood cells found in most polyps.

Dr. Tsai and colleagues focused on specificity of the liquid biopsy, noting that low specificity, or a high rate of false-positive results, would discourage the use of the screen for many individuals.

Specificity was 97.3%. Sensitivity ranged from 77% for detection of CTCs in precancerous lesions, to 87% for stage 1 - 4 cancers. Accuracy was high and ranged from 84% to 88% between precancerous and cancerous samples. Accuracy was superior to that of fecal occult blood testing.

According to coinvestigator Ashish Nimgaonkar, MD, of Johns Hopkins University, Baltimore, Maryland, survey results indicate that of patients who are reluctant to undergo colonoscopy, more than 80% would consider a blood test over stool-based tests. Dr. Nimgaonkar also indicated that the potential cost of this test is less than $100 and would be affordable, which is the number one barrier to screening.

Dr. Nimgaonkar also noted that colonoscopy would still be the gold standard diagnostic test and would be needed for tumor or polyp sample removal if an individual tests positive for CTCs.

The authors plan to validate CTC testing in the general population in Taiwan and conduct studies in the US as well. They speculate that the technology used in this study could potentially be used with other solid tumors.

Nancy Baxter, MD, PhD, of St. Michael’s Hospital, Toronto, Ontario, Canada, noted that current screening options are uncomfortable and inconvenient for patients, causing Americans to lag behind government screening goals. She hypothesized that a blood test may improve screening rates and colorectal cancer detection at earlier stages that are more likely to be cured with appropriate treatment.