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.
"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.
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.
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.
Proposed change: The American College of Obstetricians and Gynecologists says to begin screening at age 21, regardless of sexual history, and thereafter every other year. Women ages 30 and older who have three normal screens in a row need only be screened every three years.
Special cases: Women with certain risk factors - such as HIV infection, previous cervical abnormalities or exposure to the synthetic estrogen diethylstilbestrol before they were born - should consider more frequent screening.
Screening tests: Colonoscopy, fecal testing for hidden blood or immunological markers.
Recommendations: Adults aged 50 to 75 should be screened, according to the U.S. Preventive Services Task Force and the American Academy of Family Physicians. How often to get screened depends on the test: every 10 years with colonoscopy; every year with the fecal tests.
Cost: Colonoscopies cost $200 to $500, according to Medicare.
Number of people one needs to screen to save one life: No data for colonoscopy; 588 to 1,000 for fecal occult blood testing, according to Kaplan.
Adverse effects: Colonoscopies can cause injury to the colon, including pain and bleeding, although this is uncommon. Follow-up after positive results from any other test usually involves colonoscopy.
Proposed change: The American College of Gastroenterology updated its guidelines in March to say the preferred strategy is a colonoscopy every 10 years for cancer detection and prevention. (A colonoscopy allows doctors to remove any polyps found during the screen.) Previous guidelines offered a "menu" approach to the many screening options. In patients who don't want such an invasive test or for whom sedation may pose risks, it recommends fecal tests every year. Screening should begin at age 50, the college says.
Special cases: African Americans should start screening for colorectal cancer at age 45, according to the American College of Gastroenterology. People with two or more first-degree relatives (meaning a parent or sibling) who had the disease before they were 60 are also at increased risk.
Screening test: Prostate serum antigen test, digital rectal exam.
Recommendation: Medicare covers annual PSA screening in men ages 50 and up. The American Urological Assn. and the American Cancer Society do not support routine testing for prostate cancer, though they leave the decision up to doctors and patients. They urge that PSA screening, if done, be done in tandem with a digital rectal exam. The U.S. Preventive Services Task Force says there's not enough data to evaluate the risks and benefits of PSA screening in men younger than 75, but does recommend that men older than 75 should not be screened.
Cost: As cheap as a blood test or a visit to the doctor.
Number of men one needs toscreen to save one life: Data unclear.
Adverse effects: Unnecessary biopsies or aggressive treatment for a slow-growing cancer that would not have caused harm. Radiation therapy or surgery can cause incontinence, erectile dysfunction and other complications.
Proposed change: The American Urological Assn. published updated guidelines this year that avoid setting a particular PSA value at which biopsy is recommended.
Special cases: While 50 is the age most men may want to start talking to their doctors about screening for prostate cancer, men at higher risk, such as African American men and men with a father, brother or son diagnosed with prostate cancer before age 65, should start sooner.