But more people are being screened than ever before, the U.S. Centers for Disease Control and Prevention said in the first of a series of new reports on health statistics.
But, he added, "more than a third of Americans who need to be screened haven't been screened."
CDC researchers analyzed survey results from the state-level 2008 Behavioral Risk Factor Surveillance Survey for the report, available at http://www.cdc.gov/vitalsigns.
They found colon cancer screening rates rose from 52 percent of those who should get the tests in 2002 to 63 percent in 2008. Americans are advised to get a colon cancer screen, usually in the form of a colonoscopy, starting at age 50 and at age 40 if there is a family history of the disease.
A separate report found that 81 percent of women aged 50 to 74 got mammograms in 2008, virtually the same as in 2006.
"The findings indicated that more than 22 million men and women have not had a potentially life-saving screening test for colorectal cancer and about 7 million women age 50 to 74 have not had a recent mammogram," the CDC said in a statement.
"Any screening is good and the overall increase is the main message there," Frieden said. "Nevertheless, there is a lot more progress we could make with colon cancer screening."
Frieden said there are differences of opinion over how many lives could have been saved by early screening. Colonoscopies can detect and remove pre-cancerous growths before they become tumors and mammograms can catch tumors while they are small and easily removed.
The American Cancer Society says that more than 106,000 Americans were diagnosed with colon cancer in 2009 and nearly 50,000 died of it.
"What is debated is exactly how many of those would be prevented by colon cancer screening getting as high as can plausibly be expected," Frieden said.
"You can argue for 10,000. You can argue for 30,000," he added. "I think we can certainly say more than 10,000 very comfortably. For every person who dies from preventable colon cancer it is one too many."
If insurance companies stopped requiring co-payments for screening tests, that could help increase the number of people willing to be screened, Frieden said.
The report also showed that people with health insurance are far more likely to be screened for cancer, with 66 percent of those insured getting the recommended breast or colon screening compared to 36 percent of those without.
Currently, about 46 million Americans, or 15 percent of the population, has no health insurance. A new healthcare law signed in March is projected to extend coverage to 32 million more Americans, mainly by requiring them to buy it.