For years, women have been told that they needed annual Pap smears. This was an arbitrary recommendation, not based on scientific evidence, when Pap smears were initially done in the 1940s. Since scientists and doctors did not understand at the time what caused cervical cancer, and what the risk factors were, it was thought that once a year should be adequate to pick up precancerous changes on the cervix before they turned into cancer. For an interesting read on the development of the Pap test, click here:
Dr. George Papanicolaou's discovery
Fast forward about 70 years...so much more is known now about cancer in general, and specifically cervical cancer. With the knowledge we now have, it is possible to prevent cervical cancer, and even minimize risk factors for its development. Unfortunately, cervical cancer still exists, mostly for women who have not been adequately screened, or have not been appropriately treated. In 2011, over 12,000 women were diagnosed with cervical cancer in the United States, and about 1/3 of them died from it.
It has been known for many years now that cervical cancer almost always arises from infection with the human papilloma virus (HPV). There are nearly 100 strains of HPV. Some can cause annoying warts on the hands, feet, or genitalia. Some "high-risk" strains can cause cancer of the cervix, vagina, vulva, throat, penis, and anus. These high-risk strains are sexually transmitted, and it's been stated that 80% of sexually active people become infected with some strain of HPV.
The good news is that our immune systems frequently clear this virus. Most of the time, people do not get cancer from HPV. People can get cancer from HPV if their immune systems do not clear the virus. Any coexisting condition which causes the immune system not to work well (such as smoking, HIV infection, some immunosuppressive medications) also increase the risk of HPV not being cleared.
This rationale is the basis for the development of the vaccine for HPV (Gardasil or Cervarix).
We offer Gardasil in our office, which is a quadrivalent vaccine, meaning that it vaccinates against 4 strains of HPV. Types 16 and 18 cause about 70% of cervical cancer, and cause the most rapid changes to cervical cells after infection. Types 6 and 11 are responsible for the development of external genital warts. This is the first cancer that can be prevented by vaccination! Gardasil is now recommended for boys and girls ages 9-26, and is best given before the onset of sexual activity. See my HPV vaccine blog for more info...
So...back to screening. Of course I recommend the HPV vaccine, but that's only only one piece of the puzzle.
Because it takes many years (5-10) after HPV infection to cause cervical cancer, it is not recommended to screen women until 21 years of age. Often there are other reasons to see a gynecologist before that age, but not for routine Pap tests.
If a woman's Pap is negative at age 21, screening is repeated every 3 years. Why not every year?
This goes back to the fact that most often, our immune systems clear HPV. If someone has been infected with HPV, sometimes it can cause transient mild changes to the Pap that eventually resolve. If we screen annually, we are more apt to pick up those small changes. We then feel compelled to act on it, requiring biopsies, and potentially freezing or excising part of the cervix. These treatments are likely unnecessary, as mild abnormalities usually resolve on their own. If we screen every 3 years, we are less likely to find these inconsequential changes, and more likely to pick up PERSISTENT changes. These are the abnormalities we need to act on.
However, if the Pap is not normal at age 21, we do follow more closely, with more frequent Pap tests, occasional biopsies and treatments. We are not ignoring changes, just acting on those more likely to be harmful.
At age 30, the recommended approach is to add testing for high-risk HPV to routine Pap screening. Why don't we do it earlier?
Because most sexually-active women become infected with HPV, and the infection is frequently cleared, we would find a lot of high-risk HPV in the younger population that will be eventually cleared. However, if it is still present by age 30, that signifies a more likely persistent infection, which is more likely to cause pre-cancerous changes.
If the Pap and high-risk HPV test are both negative after age 30, women can safely go 5 years until their next screen. The risk of high-grade precancerous changes or cervical cancer in 5 years in this population is roughly 0.1%.
If women have had consecutive negative screens, Pap tests can be safely discontinued at age 65. Cervical cancer is different than other cancers. Because it's sexually transmitted, and takes at least 5-10 years from infection to severe changes or cancer, its peak incidence is in a woman's 30s and 40s. It is rare to diagnose cervical cancer in women over age 50 who have had adequate prior screening.
Remember that these guidelines apply to women who have had negative screening. If any abnormal result is found, we follow more closely, either with repeat Pap tests or biopsies.
Even though the Pap does not generally need to be done every year, it is still important to see your doctor annually. Much more is done at the annual well-woman exam, including breast exam, pelvic exam, check of blood pressure, height and weight, and preventive health counseling.
Much more information can be found by clicking these links:
American College of Obstetricians and Gynecologists
American Cancer Society
Centers for Disease Control
