By Debbie Saslow, PhD
When it comes to screening for cancer, a common belief held by doctors as well as patients is "more is better." It seems only logical that more frequent screening with the newest technologies translates to more cancers detected at the earliest possible time and, ultimately, more lives saved.
Cervical cancer is an example of why this is not necessarily so. Dating back to the late 1940s, the Pap test has been detecting not only early cervical cancers, but changes in the cervix ("pre-cancers") that when treated or removed lead to actual prevention of cancer in addition to early detection. For decades, the majority of women in this country have scheduled their doctor appointments around their "annual Pap." As a result of widespread Pap testing, mortality rates dropped by 70% and the Pap test became the biggest success story for cancer screening in history.
In the late 1980s, it was discovered that cervical cancer is caused by HPV, the human papilloma virus. Studies of the natural history of HPV and cervical cancer showed that it takes, on average, 10-20 years from the time a woman is first infected with HPV until the time a cervical cancer might appear.
In 1987, the American Cancer Society, and several other national organizations, recommended that most women could safely be screened for cervical cancer with the Pap test every 3 years rather than every year. Twenty-five years later, studies show that the majority of health care providers still recommend annual screenings and that the majority of women expect annual screenings.
Ten years ago, the American Cancer Society and others recommended that a new screening test, one that detects the HPV virus, could be used along with the Pap test to screen women aged 30 years and older for cervical cancer.
New cervical cancer screening guidelines
Now the American Cancer Society, working with 25 other organizations, recommends that women ages 30-65 should be screened with both the HPV test and the Pap test, called "co-testing," as the preferred strategy. (Screening with the Pap test alone every 3 years is still acceptable.)
The risk of getting cancer for a woman who is screened every 3 years with the Pap test is extremely low, and similar to the risk of cancer when screened every 5 years with both the HPV test and the Pap test. In fact, in the United States, most women who get cervical cancer have not been screened in at least 5 years. About half of them have never been screened in their lifetime.
You can see the full revised guideline here.
Guidelines often ignored
Many studies have shown that a large number of doctors screen women for cervical cancer more frequently than recommended. One recent study, for example, found that most health care providers (65%-85%, depending on the situation) not only recommend yearly Pap tests but, when screening with both the HPV test and the Pap, still recommend repeating at least 1 of the tests every year. In one situation in the study, only 14% of doctors would recommend the next test in 3 years, as guidelines recommended.
Why is this? Why have doctors been so slow to incorporate evidence-based guidelines into their practices? One reason is that many doctors think that patients want and/or expect annual screening. They may want to avoid having a discussion with patients about why this is not needed. Some may fear litigation if a cancer is missed, while others may simply be unaware of the guidelines. Lastly, there may be financial incentives to test more frequently.
Little benefit, more harm with too-frequent screening
Coming back to where we started, there is a common belief that more screening is better. In fact, annual Pap tests offer very little if any benefit compared to screening every 3 years.
But there are harms to screening more frequently. False positives are very common with cervical cancer screening, and more frequent screening leads to more frequent need for follow up tests that can be invasive and have unwanted side effects, including problems related to future pregnancies and delivery, as well as increased anxiety and time away from work or home.
With the new guidelines, the American Cancer Society recommends against annual screening.
Here are a few points to remember:
- Screening with the Pap test alone every 3 years is extremely safe and will decrease the number of false positive results without leading to an increase in cancer or cancer deaths
- For women ages 30 years and older, testing with both the HPV test and the Pap test further decreases the risk of cancer and advanced pre-cancers. When both tests are normal, no cervical cancer screening test should be done again for 5 years.
- Women younger than age 21 do not need to be screened for cervical cancer.
- Women over the age of 65 who have been regularly screened, and women who have had a hysterectomy (with removal of the cervix) for reasons not related to cervical cancer or pre-cancer, should no longer be screened.
- Women should talk to their doctors about what screening test to use and how often, and should question their doctors if they think they are being screened too often.
- Women can and should still see their doctors more often than every 3 or 5 years - just not for a Pap test. Doctor visits should be scheduled for general wellness, with Pap tests and HPV tests given according to guideline.
To see an American Cancer Society Behind the Science video detailing the new guidelines, click here.
Saslow is director of breast and gynecologic cancer for the American Cancer Society.