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Cervical Cancer: What's the Story with Screening?
With: Alan G. Waxman, MD
It's important to recognize that cervical cancer is one of the few preventable cancers, thanks to a highly effective screening test discovered by George Papanicolau, MD, in the 1950s.
"We forget that, in the 1940s and earlier, cervical cancer was a very common cancer in the United States," says Alan G. Waxman, MD, an associate professor of obstetrics and gynecology at the University of New Mexico School of Medicine in Albuquerque. Since the Pap test was first introduced, the cervical cancer rate has dropped by roughly 50 percent. But the rate is still high among minority and low-income women, who are not screened regularly.
In the last few years, new cervical cancer screening tests have been developed and new guidelines for cervical cancer screening have been released. While the new tools will help some women, studies show that most women diagnosed with cervical cancer today are those who have never been screened for it. Below, Dr. Waxman, who cowrote the American College of Obstetrics and Gynecology (ACOG) guidelines, discusses the new technologies and recommendations.
What are the primary risk factors for cervical cancer?
Cervical cancer is sexually transmitted and this has been known for a long time. What has only been appreciated over the last 10 to 15 years is that cervical cancer is caused by the human papilloma virus, or HPV.
The risk factors for cervical cancer are therefore the same as the risk factors for acquiring a sexually transmitted disease, so women who have multiple partners are more likely to come in contact with the virus. And because of the nature of the cervix, the cervix is more susceptible to HPV when women are young. Therefore, women who initiate sexual intercourse in adolescence, which is when most women in the United States do, are at increased risk.
The virus is necessary but not sufficient to cause the cancer. Which is to say, lots of women get HPV and, in most cases, their immune system gets rid of it, or at least clears it to levels that are too low for us to detect with the available technologies.
While the exposure and acquisition of the virus is necessary, the development of cervical cancer requires other factors. For instance, women who are transplant patients, who are on corticosteroid medications long-term or who have HIV are at increased risk because their immunity is suppressed.
The other thing that increases risk is smoking. Smoking seems to reduce the ability of the cervix to fight off this infection, and there have been a number of studies that show that when a woman smokes a cigarette, nicotine and the nicotine metabolites are concentrated in the cervical mucous. I always remind my patients that this is one more excellent reason to stop smoking.
Getting Pap smears on a regular basis is the principle way to bring down the cervical cancer rate, so not having access to screening is a significant risk factor. For instance, among the Lakota Indians in North and South Dakota, cervical cancer screening is not widespread. And smoking is also more prevalent in that population. So they have a much higher rate of cervical cancer and precancerous changes.
Why has the Pap test been such a good screening test?
It's an ideal screening test for a number of reasons that you could pull right out of a textbook of public health. It deals with a disease that, in the absence of the screening, is very common. Cervical cancer is the second-most common cancer among women in the world.
Number two, treatment exists once the disease is identified. Number three, it's a disease that has a very long latent period. What that means is that a woman may develop one of the precursor lesions and not develop cancer for 10 or 15 years. And that gives us numerous opportunities to intervene and prevent cancer.
Finally, the Pap test is inexpensive and it's a test that's acceptable to the general population. By comparison, if we look at screening for colon cancer, colonoscopy and sigmoidoscopy are not all that acceptable to the general population. Those are moderately uncomfortable, time-consuming and expensive procedures, and as a result they haven't been as accepted by the general population.
What does the Pap test show?
The Pap test tells the pathologist if the cells that are shed from the women's cervix exhibit the kind of changes that precede cancer, or are cancerous.
What's the difference between the conventional and the liquid-based Pap smear?
About 80 percent of Pap smears in the United States are liquid-based. They cost considerably more, but they are still relatively inexpensive. Many labs can provide a liquid-based Pap for somewhere around $30, while the conventional test costs about $10.
In the conventional Pap smear, the cells are scraped from the outside of the cervix. They are placed on a glass slide and they're fixed. When you smear it on a slide, you're smearing the mucous, the inflammatory cells and some red blood cells as well. All that extraneous material sits there on the slide along with the cervical cells, and the cytotechnologist has to pick out the correct cells to look at.
With the liquid-based Pap smear, the provider scrapes the cells from the cervix pretty much the same way and, instead of smearing it on a slide, they put it in a little vial of liquid. The liquid is prepared in such a way that the cervical cells are isolated from the extraneous debris and placed on the slide in a thin single layer of cells. There is much less clumping of cells, so it's easier for pathologists to read.
Is the liquid-based test a better test?
The answer is probably. There have been quite a few studies showing that, when you use a liquid-based system, you pick up more abnormalities. It's not so clear whether more abnormal cells actually reflects more disease. So it seems to be a better test, but we don't know how much better it is and we don't know if the increased sensitivity of the test is enough to justify the increased cost.
If you look at who gets gets cervical cancer, 50 percent of the women have never had a Pap test, so using a better Pap test won't help them. Another 10 percent are women who haven't had a Pap test in the last five years. Another 10 percent are women in whom the Pap test showed an abnormality, but they didn't get follow-up for any number of different reasons. So when you're talking about using one kind of test versus another, the better Pap test might have helped 30 percent of the women who get cervical cancer.
What is the HPV test and when is it appropriate?
The HPV test examines the cells of the cervix for the presence of the HPV virus. If the virus is not present, the chances of developing cervical cancer over the next few years are very low. The HPV test is appropriate in a few very well-defined situations. It's appropriate if women have a borderline abnormal Pap smear. Some of these Pap results represent irritation to the cervix or inflammation of the cervix that is unrelated to HPV and some represent precancerous changes. We need a way to determine which is which, and the HPV test is a helpful test there.
The American Cancer Society (ACS) and ACOG recently concluded that it may also be helpful to use the HPV test, along with the Pap smear, as a way of doing primary screening in women over 30. The beauty of it is if both the Pap smear and the HPV are negative, the woman is at an extremely low risk of having cervical cancer in the next three to five years, and the professional organizations strongly recommend that she not have further testing for another three years.
In women under 30, HPV is so common, it's not as cost-effective to screen them for HPV because the many positive results would lead to too many unnecessary cervical cancer tests.
How often should women be screened for cervical cancer?
According to the new ACS and ACOG guidelines, women should start screening about three years after they start having intercourse or at age 21. ACOG recommends annual Pap test until age 30. ACS suggests annual exams if conventional Paps are used and exams every other year if the liquid-based Pap is used. And after age 30, both recommend spacing the Paps out to every two or three years.
A woman who has had a hysterectomy and doesn't have a cervix and doesn't have cervical cancer risk factors such as a prior history of cervical cancer, DES exposure, or a suppressed immune system, does not need a Pap smear.
Common sense says that a postmenopausal woman who has had regular Pap smears all her life and has never had an abnormality is at extremely low risk of developing a new abnormality. The ACS has said low-risk women who are over age 70 don't need Pap tests any more. The U.S. Preventative Services Task Force says there's no data one way or another, but it seems reasonable to stop doing Pap tests at age 65 in well-screened, low-risk women. And ACOG hasn't come out with a distinct age cutoff.
Is there a danger that women who forgo PAP testing might not have an annual gynecological exam?
Screening for cervical cancer has, for decades, been the ticket that has gotten American women into reproductive healthcare services. When we see a patient for an annual GYN exam, we do a lot more than screening for cervical cancer. We do breast exams and examine the ovaries. We talk to them about diet, nutrition and other health factors such as sexual abuse and domestic violence, if that's appropriate, as well as sexually transmitted diseases and contraception. In older women, we talk about the transition into the menopause. So there is a lot more that goes on at the annual GYN visit than just a Pap smear and it's important for both providers and patients to know that. So if a woman's provider says she doesn't need a Pap smear for another two or three years, she still may benefit from these other services.