You'd think there could be no downside to widespread screening for cancer. But that's not always the case. Studies on Pap smears, for example, show that atypical cells can disappear if they're left alone, while interventions can cause scarring and interfere with later fertility. And many prostate cancers are so slow-growing that they won't affect a man's health, whereas cancer treatments come with adverse health effects.

Faced with the pluses and minuses, doctors often don't agree on how to screen for cancer. "Organizations send us their guidelines hoping for our endorsement," says Dr. Doug Campos-Outcalt, who heads the development of clinical practice guidelines for the American Academy of Family Physicians, an organization representing about 94,000 primary-care doctors. Those guidelines, he notes, are frequently in conflict with one another.

The American Academy of Family Physicians, for its part, tends to follow the recommendations of the U.S. Preventive Services Task Force, the group that recently advised against routine mammograms for women in their 40s. Why? Because compared with advocacy groups or specialists organizations, the task force has a far superior guideline development process that is evidence-based, not experience-based, Campos-Outcalt says.


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"Evidence-based methodology is the best," he says. "The least dependable method -- and the most likely to change -- is current practice and expert opinion."

Here's a closer look at current recommendations for breast, cervical, colorectal and prostate cancer.

Breast Cancer

Screening test: Mammogram.

Recommendation: Women ages 40 and older should be screened annually, says the American Cancer Society. The American Academy of Family Physicians says every one to two years, and the American College of Obstetricians and Gynecologists says every one to two years before age 50, and annually after that.

Cost: ranges from $90 to $150, according to Medicare and California Health Benefits Review Program.

Number of people one needs to screen to save one life:2,000 women, according to a 2009 review by the Cochrane Collaboration, an international group of experts that reviews clinical trial evidence. The recent U.S. Preventive Services Task Force analysis broke it down by age group: 1,904 women ages 40 to 49 and 1,339 women ages 50 and older.

Adverse effects: Unnecessary biopsies or diagnosing abnormalities as aggressive cancer when they're not can lead to unnecessary treatment with surgery, radiation or drugs.

Proposed changes, if any: Women ages 50 to 75 should get screened every other year and women ages 40 to 49 should not be routinely screened, according to the U.S. Preventive Services Task Force.

Special cases: Women at higher risk for breast cancer -- such as those with a mother, sister or daughter having had breast cancer, or who began menstruating before 12, or haven't borne children until age 30 (or not at all) or who have had previous breast abnormalities -- should consider getting screened in their 40s.

Cervical Cancer

Screening test: Pap smear.

Recommendation: Sexually active women up to age 65 should be screened annually, according to the U.S. Preventive Services Task Force, which studied the issue in 2003. The American Cancer Society says sexually active girls or women ages 21 to 70 should get annual screens, and the American Academy of Family Physicians recommends screening at least every three years.

Cost: $41 in California, according to the California Health Benefits Review Program.

Number of people one needs to screen to save one life: 1,140, according to Kaplan.

Adverse effects: Unnecessary biopsies or surgical removal of cervical tissue to prevent any growth of unusual looking cells found in the Pap smear. When a cone-shaped chunk of tissue is removed with methods such as the loop electrosurgical excision procedure or a laser knife, women can have problems in later pregnancies, such as premature birth or need for a cesarean delivery.