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Blood test for colorectal cancer
Cancer cells can be hard to spot |
Doctors have developed a blood test for colorectal cancer that may, in the long-term, give patients a clearer idea of whether the disease is likely to spread, or return after surgery.
The test is designed to detect the spread of cancer from the intestine to the lymph nodes by searching for a protein in the blood.
Guanylyl cyclase C (GCC) is one of seven proteins made only by intestinal cells and colorectal cancer cells.
Chief researcher Dr Scott Waldman, director of clinical pharmacology at Thomas Jefferson University in Philadelphia, said: "This is a very, very sensitive and specific test to determine whether there is microscopic disease in the lymph nodes that would otherwise escape the eye of a pathologist."
Colorectal cancer, the third most common form of cancer, is a major killer.
In some cases, colorectal cancer can be cured by surgery alone.
Human error
But as many as 40 percent of patients initially thought cured by surgery see the disease return within three years.
The researchers studied 21 colorectal cancer patients divided into two groups, one of 11 patients who had been disease-free for at least six years, and the other of 10 patients in whom the cancer had returned within three years of surgery.
Researchers found no sign of GCC in lymph node samples from the first group, but the protein was present in every patient whose cancer had returned.
Doctors currently try to determine whether colorectal cancer has spread by removing lymph nodes and examining them under a microscope to look for cancer cells.
However, this is often subject to human error, as it can be difficult to spot cancer cells if there are less than five for every 100 normal cells.
The new test is sensitive enough to detect a single cancer cell among 10 million normal cells.
Five-year study
Detection of the spread of colorectal cancer is vital as doctors do not treat patients with chemotherapy unless they have evidence that there are cancer cells in the lymph nodes.
Larger scale clinical trials are needed before the test can be routinely used by doctors.
Dr Waldman plans to enroll between 1,000 and 2,000 patients in a large, prospective five-year study comparing the ability of the standard examination of lymph nodes to that of the GCC marker test to predict recurrent disease.
Dr Lesley Walker, head of science information at the Cancer Research Campaign, said a test that could highlight the spread of colorectal cancer to the lymph nodes could potentially be "very useful".
"Many patients with bowel cancer are diagnosed after the cancer has already spread," she said.
"If bowel cancer is truly restricted to the bowel then surgery equates to almost certain cure, but it is much more difficult to treat successfully once it has spread."
However, Dr Walker warned that a lot of research was needed to establish what level of protein in the blood indicated a problem.
She said levels of another protein, Carcinoembryonic Antigen (CEA) were already used to detect bowel cancer.
The research is published in Annals of Internal Medicine.
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