Quotes of the Day

White House Press Secretary Tony Snow's announcement Tuesday that his colon cancer had returned provides a good opportunity to revisit the importance of colon cancer screening. Colon cancer is easily treated, and even cured in some cases, if lesions are caught early. The problem is that most people don't know they are harboring cancerous growths, since the disease has very few symptoms. Only a detailed look, provided by a colonoscopy screening, can pick up and remove small lesions before they become life-threatening.

In Snow's case, doctors removed his colon in 2005, and treated him with chemotherapy to eliminate any remaining cells and contain satellite growths that might have broken off from the primary tumor. After undergoing surgery to remove a growth from his right pelvic area, doctors discovered additional growths in his liver. According to Dr. Raymond DuBois, incoming provost of MD Anderson Cancer Center and a colon cancer specialist, it's not unusual to see additional growths several months or years following such a procedure. "Any time a patient comes in with a big tumor, we always worry about micrometastatic lesions somewhere else in the body," says DuBois, who did not treat Snow. "Once you have a tumor anywhere in the body, there is a chance that little seeds of metastasis may crop up later."

Fortunately, patients like Snow have more options today than ever. Until 10 years ago, there was only one drug, a chemotherapy agent, available to treat colon cancer, and it wasn't very effective. In the past decade, more chemotherapy drugs, which are easier on the body, and new classes of targeted therapies, which specifically block a tumor's ability to recruit growth factors and blood vessels, have improved the survival of patients.

But the key to containing colon cancer in people like Snow is the ability to detect recurrent tumors. Current imaging tests including MRI and PET scans may not pick up the small micrometastases that seed repeat growths; PET scans rely on the tumor's voracious appetite for glucose for energy, but until the tumor's activity reaches a certain threshold, it won't show up on the scan. So researchers are working on finding protein markers in the blood released by tumor cells that spread outside the colon; experts believe that cancer cells that venture outside the original tumor are equipped with special markers that could be detected, hopefully with something as simple as a blood test.

The best way to manage colon cancer, however, is to prevent it from getting too far. "Everybody is supposed to get screened for colon cancer right after they reach the age of 50," says DuBois, "because the risk of cancer started increasing dramatically after that. Colonoscopy is very effective; mortality rates from colon cancer have been going down in the last couple of years probably because the idea that people need to be screened is finally getting out there." When caught early, he notes, malignant growths still contained in the intestine can be removed with surgery, and 50% of patients are cured this way. About 30% of colon cancer patients, however, are diagnosed with the disease after it has progressed to more advanced stages, and spread to other organs such as the liver. "The one important message for everyone is that you don't have to go through what Tony Snow is [going through]," says DuBois.

• Alice Park
• White House Press Secretary Tony Snow's revelation that cancer has spread to his liver highlights the importance of regular screening after the age of 50