Preventing Cervical Cancer: Pap Tests, HPV Vaccines & Common Sense
By Charlea T. Massion, MD and Adriane Fugh-Berman, MD
A 59-year old physician friend of ours told us that her gynecologist sends her cards every year urging her to come in for an annual Pap test. My friend has been in a monogamous relationship for over 30 years and has had at least 20 normal Pap tests since she was 20. She feels guilty for not getting an annual Pap but, in fact, she doesn’t need one.
The Pap test is an iconic cornerstone of women’s health. Pap tests detect abnormal changes in cells from the cervix (the neck of the uterus). Some abnormalities turn into precancerous changes that, untreated, become cervical cancer. Other abnormalities detected by Paps are temporary and disappear without treatment. This low-cost, relatively low-tech test successfully detects precancerous changes early enough to save lives, and is a great screening procedure.
But here’s why the annual Pap smear should bite the dust. Health care providers used to do Pap tests every year for their female patients, no matter what. It turns out, however, that we were doing too many Paps on women who didn’t need them, and over-treating some women’s Pap results.
Cervical cancer only occurs in sexually active women who have been exposed to specific types of the human papilloma virus (HPV). Although HPV has hundreds of subtypes, only a few are associated with cancer – most notably, HPV types 16 and 18, which cause about 70 percent of cervical cancers. HPV infection isn’t enough to cause cervical cancer; about 15% of U.S. women have some form of HPV at any given time, and only a tiny percentage of those are at risk of developing cancer. Nutrition, genetics, and other unknown factors determine whether the slow progression from precancerous cells to cancerous cells occurs. Most women with HPV (including those with types 16 and 18) never develop either cervical cancer or abnormal cervical cells. In fact, almost everyone exposed to HPV cures themselves within several years of infection: about 70% of women test negative for HPV a year after their diagnosis and about 90% test negative after two years.
Women are most likely to be infected with HPV in the first three years of sexual activity. Yearly Pap tests done during this time period pick up a lot of abnormal cervical cell changes that would have vanished on their own, without treatment. Unfortunately, abnormal Pap results are likely to be aggressively treated, usually with a procedure named LEEP, which removes a chunk of tissue around the cervical opening. This weakens the area and increases the woman’s risk of having a premature birth later on. It is much better to wait and do a woman’s first Pap test three years after she became sexually active. Even then, if abnormal cells are detected, “watchful waiting” may be preferable to intervention, repeating the Pap tests rather than performing LEEP procedures. If the woman’s first Pap is normal, she should have annual conventional Paps every two years until age 30; after that, if Paps are normal, it can be done every three years.
Too many Pap tests are being done in older women as well. The U.S. Preventive Services Taskforce has suggested that it is reasonable to discontinue screening in women over 65 who have a history of normal Pap smears.(1) In many European countries, Pap screening stops at age 50, a practice which has not resulted in increased cervical cancer rates in those countries.
Another unfortunate problem with Pap tests has arisen as the way the tests are processed in laboratories. For many years, providers used a swab and/or brush to obtain cells from the cervix that were smeared onto a glass slide. A technician examined the slide under a microscope and any abnormal slides were reviewed by a pathologist. Widely used Pap screening with this method resulted in plummeting cervical cancer rates in the U.S.
In the last 10 years, however, a new, more expensive, and heavily marketed method called “liquid based cytology” (LBC) has almost completely supplanted the older technique. This would be great if LBC detected more early cervical cancers with fewer “false positives” (tests that appear abnormal but where no actual disease exists). Unfortunately, LBC actually results in more false positives than the previous method. This leads to unnecessary worry for the woman and her family, and unnecessary treatment as well.
A word about cervical cancer vaccines. No vaccine is 100% effective, and HPV vaccines do not cover all of the cancer-causing strains. Gardasil is active against only two of the HPV subtypes that cause cervical cancer (16 and 18) and two that cause genital warts (6 and 11). Cervarix, a vaccine expected to be approved in 2009, covers several more cancer-causing HPV strains but offers no protection against genital warts. Vaccinated women still need to have Pap tests on the same schedule as unvaccinated women, because the other HPV subtypes can cause cervical cancer. Cervical cancer vaccines are most effective when given before a woman becomes sexually active, although Gardasil is approved for women up to age 26 regardless of sexual history.
The Pap test is still our best protection against cervical cancer, but judicious screening can prevent unnecessary worry and unnecessary procedures.
1. U.S. Preventive Services Task Force (USPSTF), “Cervical Cancer Screening: Recommendations and Rationale,” in Guide to Clinical Preventive Services 2001-2004 (3rd Edition), Rockville: Agency for Healthcare Research and Quality, 2004. Online at: http://www.ahrq.gov/clinic/3rduspstf/cervcan/cervcanrr.htm.
Adriane Fugh-Berman, M.D., is an associate professor in the Georgetown University School of Medicine, Dept. of Physiology, and a former chair of the NWHN. Charlea T. Massion, MD, is a family physician and co-founder of the American College of Women's Health Physicians; she teaches at Stanford University School of Medicine’s Center for Education in Family Medicine.