A new report from the American Cancer Society estimates that at least half of all cancer deaths “could in principle be avoided.”

That phrase -- “in principle” -- is important. Cancer is complicated, and doctors often aren't able to say exactly why someone gets cancer. Genes, lifestyle, and exposure to cancer-causing substances are all important and may interact with each other, over time, in ways that science may not yet understand.

The American Cancer Society’s annual report isn’t about pointing fingers, casting blame, or making promises. Experts don’t have a checklist of steps guaranteed to totally prevent cancer death.

However, certain habits may help. Those practices are spotlighted in the American Cancer Society’s paper, “Cancer Prevention & Early Detection Facts & Figures 2006.”

Avoidable Risks

Some cancer risk factors can’t be changed. No one can change their genes or erase a family history of cancer. But other risk factors aren’t written in stone.

“Tobacco use, physical inactivity, obesity, and poor nutrition are major preventable causes of cancer and other diseases in the U.S.,” states the American Cancer Society’s report.

“The American Cancer Society estimates that in 2006, more than 170,000 cancer deaths will be caused by tobacco use alone,” the report continues. “In addition, scientists estimate that approximately one-third (188,277) of the 564,830 cancer deaths expected to occur in 2006 will be related to poor nutrition, physical inactivity, overweight, and obesity.”

Top 7 Tips

U.S. tobacco use is down, with per capita cigarette use at its lowest point since World War II. But obesity and inactivity are rising, the report notes.

The report makes six key suggestions:

--Don’t smoke. If you smoke now, quit, and don’t hesitate to seek help with the effort.

--Lose extra weight.

--Get regular physical activity.

--Eat healthfully.

--Limit unprotected time in the sun.

--Follow recommendations for cancer screening.

--Start as soon as possible.

Those steps may reduce risk of cancer death and other health problems, including heart disease, the American Cancer Society says.

Doctors can help with many of those strategies. For instance, it’s wise to get a doctor’s approval before starting a new fitness program, especially if you’ve been on the sidelines for a while.

Early Detection

Survival often improves when cancer is detected early. That’s why screening tests are so important.

Greater use of recommended screening tests could also help prevent “many” deaths from cancers of the breast, colon, rectum, and uterine cervix, the report states.

For example, the American Cancer society notes that “fewer than half of Americans for whom [colorectal cancer] testing is recommended have had a recent screening test.”

The report shows increases in screening rates for cervical and breast cancers over the past decade. But it also shows room for improvement:

--45 percent of women aged 40 and older haven’t gotten a mammogram in the past year Nearly 1 in 5 adult women hasn’t had a Pap test in the past three years.

Mammograms screen for breast abnormalities; follow-up tests are needed to diagnose breast cancer. Pap tests sample cervical cells to look for cervical cancer or abnormalities that may lead to cervical cancer.

Screening rates tend to be worse in people with lower income and education levels, the uninsured, and new immigrants, the report notes.

American Cancer Society’s Test List

The report includes a brief overview of routine cancer screening for those at average risk:

Breast:Yearly mammograms starting at 40 for women. Clinical breast exams during routine checkups for women, starting in their 20s.

Colon and rectum:Screening for all people starting at age 50.

Prostate:Digital rectal exam and prostate-specific antigen (PSA) test should be offered annually to men, starting at 50. Men at high risk, including black men, should begin testing at 45.

Cervix:Screening should start about three years after a woman starts having vaginal intercourse, but no later than age 21.

Cancer-related checkup: For people who get periodic health exams, a cancer-related checkup should include health counseling, and, depending on the patient’s age and gender, might include tests for cancer of the thyroid, mouth, skin, lymph nodes, testes, ovaries, and some nonmalignant diseases.

Talk to your doctor about those recommendations. For instance, the CDC’s advice on mammograms is slightly different. The CDC recommends that women aged 40-74 get a mammogram every one or two years, with or without clinical breast exam.

People at higher risk of cancer may need screening sooner than others, and no test is perfect. Your doctor can help create a test schedule that fits your health profile.

By Miranda Hitti, reviewed by Louise Change

SOURCES: American Cancer Society: “Cancer Prevention & Early Detection Facts & Figures 2006.” WebMD Medical Reference provided in collaboration with The Cleveland Clinic: “Sexual Health: Pap Smear.” CDC: “Breast Cancer and Mammography Information.” News release, American Cancer Society.