Digestion : Blood Test for Colon Cancer Screening

By David Templeton, Pittsburgh Post-Gazette

Colonoscopies are used successfully to screen for colorectal cancer and save lives. But many people are reluctant to go through the ordeal despite less than 10 percent survival rate for those with advanced cancer versus a 90 percent survival rate for those whose cancer was detected early.

A South Korean study could help in boosting the number of people who are screened with a potential new blood test to detect the cancer at any stage of development, including early stages.

Published June 7 in the Journal of Molecular Diagnostics, the study identifies biomarkers for colorectal cancer that show up in blood serum and reveal the presence of the cancer.

The study notes "surprisingly low" willingness in the general public to undergo colonoscopies, due to the extensive bowel preparations that many find to be prohibitive, along with the discomfort of the outpatient procedure.

A noninvasive test of a blood sample would be "an attractive alternative for screening of people who are advised to have a colonoscopy," the study states.

The research focused on an aberrant genetic process of DNA hypermethylation, which deactivates a group of genes that suppress tumor cells that develop consistently in the body. Blocking those genes allows colorectal cancer and other cancers to develop.

Recent studies have shown that cancer-specific biomarkers can be detected in blood samples from patients with various solid tumors, including colorectal cancer, according to the study. The Korean team has identified a novel gene that represents a promising marker for cancer detection.

Validation studies of blood and tissue involved 120 people, including a group with various stages of colon cancer and another group having no cancer. The research demonstrated that the gene found in blood and tissue specifically indicated the presence of colorectal cancer. Further development and testing would be necessary to prove the method to be valid as a blood test for cancer detection.

The fact the biomarker is frequently detected in all stages of the cancer heightens its potential. "We have successfully identified a novel gene SDC2 as a sensitive and specific marker for the remote detection of early stage colorectal cancer in a small volume of serum," the researchers say.

The colonoscopy represents the gold standard for early identification of the cancer.

The study says a noninvasive diagnostic tool, such as a blood test for a cancer biomarker, could be used as an alternative to, or in conjunction with, a colonoscopy. If the blood test shows evidence of cancer, it could be followed with a colonoscopy to confirm its presence and stage.

Sherif L. Rizk, clinical director of West Penn Allegheny Health System's division of colorectal surgery, described the study as "a very exciting finding if the results can be duplicated and confirmed."

"More people are more likely to have blood drawn than have a colonoscopy to test for colorectal cancer," he said. While unanswered questions remain, the study has piqued interest in doing follow-up clinical studies, Dr. Rizk said. Another question to be answered, he said, is whether the test can determine the presence of precancerous polyps in the colon, which readily are detected and removed during most colonoscopies.

The U.S. Centers for Disease Control and Prevention reports that 40 percent of adults 50 to 75 years old haven't been screened for colorectal cancer, which the CDC recommends people to have done once every 10 years.

"People who do not have health insurance or a usual source of health care were the least likely to be screened," the CDC states. "Also, many people don't know they need to be screened for colorectal cancer."

A colonoscopy requires the patient to go on a clear liquid diet the day or evening before the outpatient procedure while typically drinking a gallon of solution that empties the bowels. The procedure itself also can be uncomfortable, even painful.

Colorectal cancer is one of the most common types of malignancies worldwide and a known major cause of cancer morbidity and mortality. The mean five-year survival rate for colorectal cancer is estimated to be less than 10 percent if metastasis occurs, but it could be as high as 90 percent if the cancer is detected at an early state.

Two other screening methods -- the fecal occult blood test and the fecal immunochemical test -- are used to detect the cancer but are not as accurate as the colonoscopy nor as convenient as a blood test.

Of the major cancers affecting both men and women, colorectal cancer is the second leading cause of cancer-related deaths in the United States and the third most common cancer, the CDC reports. In 2009, the most recent year for available data, 136,717 people in the United States were diagnosed with the cancer -- 70,223 men and 66,494 women.

That year, 51,848 people nationwide died from the cancer, with men representing 52 percent of that total.

David Templeton: dtempleton@post-gazette.com or 412-263-1578 .

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