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SAN FRANCISCO -- A liquid biopsy detected circulating tumor cells (CTCs) associated with colorectal cancer with overall accuracy approaching 90%, according to a study reported here.

The test's accuracy varied according to the stage of the disease, including 77% sensitivity for detection of precancerous lesions in the colon. The test had sensitivity exceeding 97%, reflecting a low probability of false-positive result.

If the results hold up in additional testing, the liquid biopsy might offer another option for colorectal cancer screening, Wen-Sy Tsai, MD, of Linkou Chang Gung Memorial Hospital in Taoyuan, Taiwan, reported at the Gastrointestinal Cancers Symposium.

"There is still some reticence among patients to use stool-based tests or have an invasive exam like colonoscopy to detect colorectal cancer," Tsai said in a statement. "Our results may point to a solution for people who are reluctant to get an initial screening colonoscopy or are not compliant in returning stool-based test kits that they get from their doctors."

Several recent studies showed that more than 80% of patients who are reluctant to undergo colonoscopy would find a blood test acceptable, said co-author Ashish Nimgaonkar, MD, of Johns Hopkins University in Baltimore. Other studies showed that affordability remains the biggest obstacle to colorectal cancer screening for most people; a liquid biopsy for CTCs might cost less than $100, he added.

Inconvenience, discomfort, and cost all contribute to Americans' reluctant to undergo colorectal cancer screening, agreed Nancy Baxter, MD, PhD, an American Society of Clinical Oncology expert in gastrointestinal cancers.

"Thought this research needs more investigation, a simple, accurate blood test could help increase screening rates, which could ultimately improve detection of colorectal cancers at earlier stages when treatment is most likely to be curative," said Baxter, of the University of Toronto and St. Michael's Hospital.

The study involved 620 adult Taiwanese patients with scheduled routine colonoscopy or colonoscopy for follow-up of confirmed colorectal cancer. Colonoscopy and biopsy confirmed that 111 of the patients had adenomatous polyps and 327 had colorectal cancer, ranging from early- to late-stage disease. The remaining 182 patients had no evidence of adenomas or colon cancer and served as a comparison group.

The liquid biopsy required each patients to provide 2 mL of blood, which was analyzed by a test with proven ability to identify a single CTC within 1 billion cells from an adenomatous polyp. Results were compared with the colonoscopy findings by reviewers who had no prior knowledge of the findings of either test.

Using colonoscopy findings as the definitive result, investigators found that the blood test had an overall accuracy of 88%. The test had a sensitivity of 84.0% among the 182 study participants without adenomas or colorectal cancer, 76.6% for participants with adenomatous polyps, and 86.9% for the patients with colorectal cancer. The test results yielded a specificity of 97.3% in the cancer-free group, the polyp group, and the patients with confirmed colorectal cancer.

"We believe our high specificity results are important because a high number of false-positive results would discourage many people who are considering getting screened for colorectal cancer from doing so," said Tsai.

Performance analysis showed the test had an area under the curve of 0.87 for the control group, 0.84 for the participants with polyps, and 0.88 for the patients with colorectal cancer.

Following approval of the Cologuard stool DNA test for colorectal cancer screening, gastroenterologists and colon cancer specialists noted the test's poor performance for detecting adenomatous polyps. In the randomized comparing against fecal immunochemical testing that supported the FDA application, the DNA test detected 92% of colon cancers versus 42% of adenomatous polyps. The study also yielded a 13% rate of false-positives for the DNA test.

Moreover, as one gastroenterologist noted in an opinion piece for MedPage Today, no currently available screening test will replace colonoscopy as the gold standard for diagnosis of colorectal cancer. Even if the initial results with the liquid biopsy hold up in additional testing, the CTC test colonoscopy will remain the standard for definitive diagnosis and to guide biopsy of a tumor or removal of a polyp detected by the liquid biopsy, Nimgaonkar noted.

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