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Diagnosing Cancer

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Mammograms: To screen or not to screen?

The mammography debate rages on, newly fueled by results from a Canadian trial published in the Sept. 3, 2002, Annals of Internal Medicine.

The Canadian National Breast Screening Study (CNBSS) is the first trial designed specifically to assess screening mammography in women ages 40–49. In the early 1980s, the CNBSS recruited 50,430 women in this age group with no history of breast cancer. Half were assigned to receive annual mammograms; the other half, to receive “usual care,” meaning that mammograms were done only if a patient’s doctor recommended them.

After an average of 13 years, there were 105 breast cancer deaths in the mammography group and 108 in the usual care group — not statistically significant difference. The researchers concluded that mammograms are not justified for breast cancer screening in women under age 50.

Critics of the CNBSS trial said the data came from older technology, before improved imaging was available. The women who took part enrolled 20 years ago, when mammography images were less clear and radiologists weren’t as proficient at reading them.

But the American Cancer Society, the Centers for Disease Control and Prevention, and the National Cancer Institute advise women to get annual mammograms starting at age 40.

To further muddy the waters, the same issue of Annals of Internal Medicine that carried the CNBSS results published new guidelines for breast cancer screening from the U.S. Preventive Services Task Force (USPSTF). The USPSTF is a panel of health experts that analyzes published research and makes suggestions about preventive health care.

The group recommends having a mammogram every one to two years, starting at age 40. The authors assert that there is no convincing evidence to support the theory that starting annual screening at age 40 exposes women to undue harm, with minimal chances of finding cancer.

On the other hand, if mammograms can find breast cancer, why not start at age 40? For one, the screening test may adversely affect some women. False-positive results (which flag a problem when none exists) can lead to anxiety and further testing.

In defense of its recommendations, however, the USPSTF says that anxiety usually disintegrates after cancer is ruled out. And even when it doesn’t go away, anxiety doesn’t seem to discourage women from continuing their screening regimen.

If you have a family history of breast cancer or other risk factors, it makes sense to start mammograms at age 40 (perhaps earlier, depending upon your level of risk). For everyone else, a discussion with your doctor is the most sensible first step. If she or he feels annual mammograms are unnecessary for you, and you’re comfortable with the decision, waiting until you’re 50 should be fine.

November 2002 Update

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A New Approach to Testing for Cervical Cancer

Most women know that regular Pap smears can almost eliminate the chances of developing invasive cervical cancer. By examining the cervix for abnormal (and potentially precancerous) cells, treatment can be started before a real problem develops.

What many women may not know is that human papilloma viruses (HPVs) (which cause genital warts) are responsible for the majority of cases of cervical cancer. Two recent studies suggest that regular screening for HPV may prove even more effective than the traditional Pap smear in preventing cervical cancer.

The first study included 8,554 women who lived in the Gaunacaste Province of Costa Rica, where there is a very high rate of cervical cancer. Researchers found that HPV testing picked up 17% more high-grade cervical cell abormalities and cancers.

The second study compared the Pap smear with testing vaginal samples for HPV. 1,415 women in South Africa (who had not had any cervical cancer screening) participated. The first HPV test was done by a doctor during a routine physical exam. The HPV test was done on samples of vaginal fluid the women collected themselves using a cotton swab. All the women had Pap smears done as well. The HPV testing on samples taken by the doctor detected far more cervical disease than the Pap smear (84% vs. 68%). The HPV testing done on the self-collected samples was not equivalent to the HPV tests done on the physician-collected samples, but was just as good as the Pap smear. And did not require a trip to the doctor’s office.

What are the important take-home messages from these studies? First, each year in the United States there are an estimated 15,000 new cases of cervical cancer. Each year, about 5,000 women will die needlessly of the disease. Regular Pap smears are the most effective way to screen for this disease. Second, although HPV is one of the most common sexually transmitted infections, only a small number of women suffer complications, including cervical disease. There are over 70 types of HPV, but only 13 are known to cause cervical cancer.

Still, screening techniques that include HPV testing may not only increase the ability to detect abnormal cell changes early, but can also let a woman know whether or not she carries one of the more dangerous viruses (and therefore needs to be extra vigilant about screening). Finally, self-collected samples for testing may take us a big step forward in preventing this disease in places where women do not get regular visits to the doctor.

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