The Pap test, or Pap smear as it
has been called, has been the primary screening tool for cervical cancer in the United States and around the world for over half a century, but some experts argue it is time for new tests to take over.
We now know that 70 percent of cervical cancer cases are
caused by two strains of the human papillomavirus (HPV), and have tests that can detect these two strains in a sample of cervical cells. Such tests are currently used in conjunction with the Pap test for some patients, or after a Pap test shows abnormalities in others.
Last week, a Food and Drug Administration (FDA) review panel voted unanimously to allow one HPV test to be used by itself as a primary screening tool in women age 25 and older.
Invented in 1928 by Greek physician George Papanicolaou, the Pap test scrapes cells from a woman’s cervix, which are then examined under a microscope by a cytologist who looks for abnormalities. According to experts, precancerous cells have a “halo” around them and cancerous cells have a colorful nucleus. The Pap test allows physicians to catch and treat cervical cancer before there are any symptoms or, even better, to detect precancerous cells and provide treatment that can prevent cancer from ever developing. The test is credited with reducing the death rate from cervical cancer in the United States by over 70 percent between 1955 and 1992 alone.
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In recent years, Pap tests have often been combined with or followed up by HPV screening tests, because it has become clear that the most cervical cancer is caused by HPV, a highly contagious sexually transmitted infection. It is estimated that 79 million Americans are infected with HPV. Many people may never know they have the virus, as their immune system is able to clear it before it causes any adverse health effects. Some people, however, will get genital warts, while others may develop cancers of the cervix, penis, anus, or throat. As mentioned earlier, researchers have concluded that two strands of HPV (16 and 18) are responsible for 70 percent of all cervical cancers. The HPV test that the FDA panel voted on last week, which is called the Cobas test and was developed by the drug company Roche, specifically looks for these two strains.
In recent years, cervical cancer rates in the United States have leveled off, with approximately 12,000 cases and 4,000 deaths anticipated for 2014
. Experts acknowledge that most cases of cervical cancer occur in women who have not been screened at all or in many years. Still, some argue that better screening tests will help, and believe that the Cobas test is better in part because it takes the objectivity out of the process. Instead of a person looking at cells under a microscope, this test is done by machine, which means less variation in results from lab to lab. Studies have also shown the test to be more sensitive to detecting precancerous lesions than a traditional Pap test.
The current guidelines suggest that women between the ages of 21
and 30 have a Pap test every three years, while women ages 30 to 65, who are more likely to have precancerous lesions, get both a Pap test and an HPV test every five years or just a Pap test every three years. The panel was asked to weigh in on whether the HPV test could be used instead of the Pap or the combined tests in all women over 25. Arguing in favor of the change, Lee Shulman, a professor at Northwestern, told the committee that this was like changing from horses to cars. He added, “George Papanicolaou didn’t know about HPV.”
The panel agreed, voting unanimously for the change. The next step is for the FDA to accept the panel’s recommendation. Even if it does, however, it is unlikely that the Pap test will disappear any time soon. Though physicians will have the option of using the Cobas test alone, most will likely stick with the testing guidelines recommended by professional medical groups such as the American Congress of Obstetricians and Gynecologists (ACOG), and these groups often take longer to make changes.