Jan. 24 (HealthDay News) -- Researchers say they have zeroed in on a biomarker that could detect colorectal cancer in its earliest stages in a simpler, less invasive and more accurate way than existing blood tests.

The marker, called colon cancer-specific antigen-2 (CCSA-2), could also differentiate between early- and late-stage disease, the researchers added.

The study was one of several concerning colon cancer being presented at the annual Gastrointestinal Cancers Symposium being held Jan. 25 to 27 in Orlando, Fla.

A second study found that patients who are uninsured or who have coverage with Medicaid tend to be diagnosed with colorectal cancer at a later stage than individuals with private insurance or Medicare. This is the first nationwide survey to confirm similar findings from smaller polls.

And a third study is a step on the road to so-called personalized medicine. "This study assesses the benefit of treatment with a monoclonal antibody for colorectal cancer patients based on their tumor's molecular signature," Dr. Nicholas Petrelli, an official with the symposium, said during a Wednesday teleconference on the findings.

According to the American Cancer Society, colorectal cancer is the third most common cancer among American men and women. Some 150,000 new cases are diagnosed each year in the United States.

Regular screening can catch the disease while it is still curable. Colon cancer can also be prevented if polyps and adenomas are found and removed before they become malignant.

There are already blood tests for colorectal cancer, but they result in false-positives in 60 percent to 90 percent of cases, depending on the test, said the authors of the first study.

The researchers, from Johns Hopkins University and the University of Pittsburgh, looked at 135 blood samples from individuals who had undergone colonoscopies. They were compared with samples from individuals with other types of cancer or with benign diseases.

Only about 20 percent of results were false positives, while only 9 percent of cancers went undetected.

There was also a correlation between the level of CCSA-2 in the blood and the size of the growth. The highest levels of CCSA-2 indicated the presence of actual cancer. The study was funded by Onconome, which has licensed the patent for the test from the University of Pittsburgh researchers.

The second study, conducted by the American Cancer Society, found that patients without health insurance were almost two times more likely and Medicaid patients 40 percent more likely to be diagnosed with stage II colon cancer rather than stage I disease, compared to those with Medicare or private insurance.

And again, uninsured patients were twice as likely while Medicaid patients were 50 percent more likely to be diagnosed with stage III or IV colon cancer than patients in the other insurance categories. The results held steady no matter where the cancer was found.

Minorities, females, older patients, those who lived in areas with low-income and low-education levels and those who were treated at non-research teaching hospitals were more likely to be diagnosed with advanced cancer.

"Improved access to screening and medical care in these populations may be able to reduce these disparities," said study author Dr. Michael Halpern, strategic director of health services research at the American Cancer Society.

And the third study confirmed that only patients who have a normal form of the KRAS gene in their tumors will benefit from the monoclonal antibody Vectibix (panitumumab). Mutations are found in 30 percent to 50 percent of colorectal cancer patients. The study was funded by Amgen, which makes the drug.

SOURCES: Jan. 23, 2008, teleconference with Nicholas Petrelli, M.D., official, Gastrointestinal Cancers Symposium; Michael T. Halpern, M.D., Ph.D., strategic director, health services research, American Cancer Society