A test measuring circulating tumor cells (CTCs) in the bloodstream was able to accurately detect early-stage colorectal cancers, according to the results of a study presented ahead of the 2018 Gastrointestinal Cancers Symposium, held January 18–20 in San Francisco. The test, sometimes called a liquid biopsy, was able to detect colorectal cancer at an early stage with an accuracy between 84% and 88%.
“Our study is important because there is still some reticence among patients to use stool-based tests or have an invasive exam like colonoscopy to detect colorectal cancer,” said lead study author Wen-Sy Tsai, MD, assistant professor at the Linkou Chang Gung Memorial Hospital, Taipei, Taiwan. “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.”
For the study, the researchers enrolled 620 people aged 20 or older who came to the Chang Gung Memorial Hospital in Taiwan for routine colonoscopies or who had a confirmed colorectal cancer diagnosis. All participants had 2 mL of peripheral whole blood tested for CTC analysis through a routine blood draw. The blood samples were processed using CMx, an assay that captures rare CTCs—such as those found in early-stage cancer—on a lipid-coated chip that mimics human tissue. The results of these assays were then compared in a blinded analysis with the colonoscopy results.
Using the colonoscopy or biopsy results, 438 people were diagnosed with either adenomatous polyps or early- to late-stage colorectal cancers. The specificity value of the CTC test was 97.3%, indicating a very low probability of a false positive result.
According to Dr. Tsai, the 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.”
Sensitivity results for the test ranged from 77% for detection of CTCs in precancerous lesions to 87% for stage I–IV cancers. Taking into account both sensitivity and specificity, the researchers calculated that the test had an accuracy between 84% and 88% between precancerous and cancerous samples.
“Recent surveys have found that over 80% of patients who are reluctant to undergo colonoscopy screening would be receptive to a blood test over stool-based tests,” said coauthor Ashish Nimgaonkar, MD, assistant professor of medicine at Johns Hopkins University in Baltimore, Maryland. “A number of studies have found that affordability was the number one reason for not being screened, however this test is highly affordable and can potentially cost less than $100.” 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 had a positive CTC test.
Commenting on the results of the study, Nancy Baxter, MD, and American Society of Clinical Oncology (ASCO) expert in gastrointestinal cancers wrote, “Screening for colorectal cancer can be lifesaving, but Americans still lag behind Federal government screening goals because current screening options can be inconvenient and uncomfortable for patients. Though 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.”