The blood-based biomarker colon cancer-specific antigen-2 may be useful for early detection of advanced adenomas and colorectal cancer, according to a presentation at the 2008 Gastrointestinal Cancers Symposium.

The goal of the current work was to find an accurate, simple and noninvasive method for early detection of colorectal cancer. There are other noninvasive tests for colorectal cancer, including the carcinoembryonic antigen test, but the researchers had noted that the other tests lack specificity, resulting in false positives in about 85 to 90 percent of cases for the fecal occult blood test and about 40 to 60 percent for the carcinoembryonic antigen test.

"Our goal when researching colorectal cancer biomarkers was to take a step back and try to understand the fundamental properties of the cancer cell," said Eddy S. Leman, PhD, instructor in the department of urology at Johns Hopkins Hospital. "The theory was that there must be a set of proteins that correlate with the changes that are seen when a cell becomes cancerous and are specific to colorectal cancer. With CCSA-2, we've found a biomarker that not only better detects the presence of colon cancer, but also may accurately indicate whether a patient has a high-risk precancerous condition."

Researchers analyzed 135 blood samples from patients who had undergone colonoscopies and had been diagnosed as normal (24 percent), with potentially precancerous growths (polyps: 19 percent; nonadvanced adenomas: 29 percent; advanced adenomas: 14 percent), or colorectal cancer (14 percent). A control population of 125 people, made up of individuals with benign diseases or other types of cancer, was also included.

Leman and colleagues previously demonstrated that the proteins colon cancer-specific antigen-3 and -4 (CCSA-3 and CCSA-4) can indicate the presence of colorectal cancer. The CCSA-2 immunoassay, however, is unique because in addition to detecting cancer, researchers noted a direct correlation between the level of biomarker in the blood and the size of adenomas: the higher the level of biomarker in the blood, the larger the growth; the highest levels of the biomarker indicated the presence of colorectal cancer.

The researchers could distinguish patients who had colorectal cancer or advanced adenomas from those who had nonadvanced adenomas, low-risk polyps or normal colons.

CCSA-2 also had a lower rate of false positives than CCSA-3 and CCSA-4.
The test had an overall specificity of about 80 percent and a sensitivity of 91 percent.

Based on these results, the next step is to validate the findings with larger groups of patients at a greater number of research institutions.