Many people with colon cancer may not be diagnosed until after symptoms arise, even though the disease can be caught earlier with routine screening, a study released Monday suggests.

In an analysis of data from a large U.S. cancer registry, researchers found that more than half of older adults with colorectal cancer had a disease-detecting procedure within 6 months of their diagnosis - making it likely that the procedure was performed not as part of routine screening, but as a diagnostic test spurred by colon cancer symptoms.

Forty-four percent of the nearly 6,000 patients had a test - such as fecal occult blood testing (FOBT) or colonoscopy - more than 6 months before their cancer diagnosis. In these cases, the procedures were probably done as part of colon cancer screening, study co-author Dr. Gregory S. Cooper told Reuters Health, and patients in this group were more likely to be diagnosed at an earlier stage in the disease.

“This is another piece of evidence that screening is beneficial,” said Cooper, a gastroenterologist at Case Western Reserve University and the University Hospitals of Cleveland.

But the findings, being published in the journal Cancer, also provide yet more evidence that colon cancer screening is underused in the U.S, according to Cooper and colleague Jonathan D. Payes.

Medical groups such as the American Cancer Society advise that adults at average risk of colon cancer begin routine screening for the disease at age 50, with the frequency depending on which test doctors and patients choose.

FOBT, which detects hidden blood in stool samples, is the least sensitive test, and experts recommend that it be done every year - preferably in combination with a sigmoidoscopy procedure every 5 years. Another option is to have a colonoscopy every 10 years.

Sigmoidoscopy and colonoscopy both involve inserting a thin, flexible scope into the colon to look for cancer or polyps, which are growths that can become cancerous. Sigmoidoscopy investigates only the lower portion of the colon, while colonoscopy inspects the entire length of the colon.

Colonoscopy is considered the most sensitive way to screen for colon cancer, Cooper noted, though many people balk at having the procedure and not all insurance plans cover the test when it’s used for screening.

Colonoscopy cannot only detect cancer, Cooper said, but can also prevent it by allowing doctors to find and remove polyps.

In his team’s study, which looked at data on 5,806 U.S. adults age 70 and up who were diagnosed with colorectal cancer in 1999, colonoscopy was the most frequently performed procedure.

However, most of those exams were done within 6 months of patients’ diagnoses, which indicates they were often performed as a diagnostic test for suspected cancer - and not as part of routine screening.

In contrast, when the researchers looked at the 44 percent of patients who’d had a procedure more than 6 months before their cancer diagnosis, FOBT was the most commonly performed procedure. Six percent of these patients had a colonoscopy.

Most importantly, Cooper’s team found, these 44 percent of patients - who were most likely to have gotten tests for screening purposes - were less likely to be diagnosed with colon cancer at a more-advanced stage.

That means, Cooper said, that these patients were also likely to have better survival rates.

SOURCE: Cancer, February 15, 2005.