Although most experts agree that as many as two-thirds of cancer cases are caused by lifestyle choices like smoking, poor diet and lack of exercise, the two-member panel said many avoidable cancers were also caused by pollution, radon gas from the soil and medical imaging scans.

Some of the advisers' points are not in dispute. Several government-sponsored reports have pointed to cancer risks from X-rays and CT scans, and industry and physician groups are already working on ways to lower the doses given to people.

Radon has been a known source for decades, and the Food and Drug Administration and National Institutes of Health are studying the possible effects of the common plastics ingredient bisphenal A or BPA.

But other points have little science to back them.

For instance, the panel said that since so little is known about the potential risks of cell phones, people would be prudent to wear headsets and make calls quickly. Many large studies have found no links between cell phone use and cancer.

The panel was particularly concerned to find that the true burden of environmentally induced cancer has been grossly underestimated, reads the report, available at www.pcp.cancer.gov.

The report is sure to stun industry and many cancer specialists. It has already delighted environmental groups, which have had hints for more than a week of the report's content and scheduled news conferences for later on Thursday.

The American Cancer Society said the report downplayed known risks that cause most cases of cancer including tobacco, obesity, alcohol, infections, hormones and sunlight.

HYPOTHESIS AS FACT?

The report is most provocative when it restates hypotheses as if they were established facts, the society's Dr. Michael Thun said in a statement.

For example, its conclusion that 'the true burden of environmentally (pollution) induced cancer has been grossly underestimated' does not represent scientific consensus.

The National Cancer Institute -- whose logo is on the report -- had almost nothing to say.

As the panel is charged with sending a report directly to the president and I don't believe that anyone at NCI has had a chance to review the report yet, we will probably not have an immediate comment, spokesman Mike Miller said by e-mail.

The two sitting members of the panel -- the third seat is empty -- are Dr. LaSalle Leffall, professor of surgery at Howard University College of Medicine in Washington and Margaret Kripke, an emeritus professor at the University of Texas M.D. Anderson Cancer Center.

Cancer is the No. 2 killer of Americans, after heart disease.

The incidence of some cancers, including some most common among children, is increasing for unexplained reasons, the report reads.

With nearly 80,000 chemicals on the market in the United States, many of which are used by millions of Americans in their daily lives and are un- or understudied and largely unregulated, exposure to potential environmental carcinogens is widespread, it adds.

The American people -- even before they are born -- are bombarded continually with myriad combinations of these dangerous exposures, Kripke and Leffall wrote in a letter to President Barack Obama at top of the report.

The panel urges you most strongly to use the power of your office to remove the carcinogens and other toxins from our food, water, and air that needlessly increase healthcare costs, cripple our nation's productivity, and devastate American lives.

Medicine Cancer