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In a step that might eventually make colon cancer easier to detect and treat, a study published today in the journal Cancer Research finds that the immune system naturally identifies the hallmark signs of this cancer. Compared to 75 healthy adults, nearly half of colon cancer patients studied showed exclusive immune reactions to one of 13 specific tumor markers, or antigens, which can be found through a simple blood test.

"In the future, we may be able to find more antigens that cancer patients react to," said Dr. Mathew Scanlan, Assistant Member of the Ludwig Institute for Cancer Research, New York Branch at Memorial Sloan-Kettering, and lead author of the study. "It could then be possible to harness the immune systems own ability to detect disease and use it as a diagnostic tool."

In an effort to develop simpler and less invasive methods for detecting cancer, researchers have generally focused on measuring one specific cancer antigen that circulates in the blood. Although no such test is routinely used for colon cancer, similar strategies are used to detect other types of cancer, such as the prostate specific antigen (PSA) test for prostate cancer and CA125 test for ovarian cancer.

But cancer antigens can be difficult to spot because of they are present in such small amounts. The immune system, on the other hand, is naturally adept at finding even the tiniest clues of disease. By measuring how antibodies react to several tumor antigens at once (each antibody reacts to a specific antigen and they are also found in the blood), this new approach might be a highly sensitive and easy way to detect cancer.

"Such tests would complement regular screening methods and might help avoid misdiagnoses as well," said Dr. Scanlan.

For the study, Dr. Scanlan and his team screened for antibody reactions to 77 tumor antigens previously discovered by a method called SEREX (serological analysis of recombinant cDNA expression). There were no antibody reactions found in a group of healthy volunteers.

However, blood samples from 34 of 74 (46%) colon cancer patients detected reactions to one or more of the 13 specific colon cancer antigens, with the most frequent responses showing up in the earlier and later stages of disease. Nearly 70% patients with stage I colon cancer had an immune response to one of these antigens, while more than 50% with stage IV disease did.

The team also found groupings of colon cancer antigens that may turn out to be attractive targets for highly selective anti-cancer drugs or vaccines.

"Based on a patients own specific tumor profile, we could design treatments that go after the best targets without harming healthy tissue," said Dr. Scanlan. "What we need to do now is find more antigens."