A new study has found that a test that identifies circulating tumor cells (CTCs) present in the bloodstream can detect colorectal cancer at an early stage, with accuracy ranging from 84 to 88%. Most prior studies using CTCs have been able to detect late-stage colorectal cancer, and this study is one of the first clinical studies to show that CTCs can be useful for detecting early, more treatable stages of the cancer. These findings were presented at the 2018 ASCO Gastrointestinal Cancers Symposium in San Francisco, California.

CTCs break away from the primary tumor and travel into the bloodstream where they can then form new tumors at distant locations. Collection of CTCs from the blood is one form of "liquid biopsy".

"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, 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."

This study was conducted at Chang Gung Memorial Hospital, Taoyuan, Taiwan. The researchers enrolled 620 people over the age of 20 who were coming to the hospital for routine colonoscopies or had a confirmed colorectal cancer diagnosis. Based on the colonoscopy and biopsy, 438 people were found to have either adenomatous polyps or early to late-stage colorectal cancers. The remaining study participants had no signs of a pre- cancerous growth or colorectal cancer (comparison group).

All 620 enrollees had 2 milliliters of 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. In prior studies, this assay was found to be able to detect very small numbers of CTCs, even down to the level of one CTC per billion blood cells found in most polyps. The researchers focused on specificity of the liquid biopsy test. "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. The specificity values were 97.3%, indicating a very low (less than 3%) probability of a false-positive result.

The study results showed that sensitivity ranged from 77% for detection of CTCs in pre-cancerous lesions, to 87% for stage I-IV cancers. The researchers also calculated the accuracy of the results, which takes into account both sensitivity and specificity, and found that the accuracy of the test was high and ranged from 84 to 88% between pre-cancerous and cancerous samples. The accuracy of this test was superior to that of fecal occult blood testing (FOBT).

"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 co-author Ashish Nimgaonkar, MD, assistant professor of medicine, Johns Hopkins University, 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.

"Screening for colorectal cancer can be life-saving. Though this research needs more investigation as 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 Nancy Baxter, MD, ASCO Expert in gastrointestinal cancers.

The authors are currently planning to validate the use of CTC testing in the general population in Taiwan and to conduct studies in the U.S. According to the authors, the technology used in this study potentially could be used with other solid tumors, such as breast, lung, and prostate cancer.

This study was sponsored by the Ministry of Health in Taiwan and Chang Gang Memorial Hospital.