The pap smear is a screening test for abnormal cells of the cervix. It is a great screening test because it can prevent the development of cervical cancer. The pap smear was developed in the 1940’s by Dr. George Papanicolaou. It was in general usage by the 1950’s. Initially recommended every year, the pap smear was a resounding success. The incidence of cervical cancer in the United States decreased by over 60% after the advent of the pap smear. The pap smear does not check for uterine cancer, ovarian cancer or any other disease.
Pap smears are a screening test and have a pretty high rate of false negatives (meaning there are abnormal changes of the cervix that were not detected) and a pretty high rate of false positives (meaning the cervix is normal but the pap smear comes back abnormal). If pap smears were perfect at picking up disease, meaning that a negative one meant we knew for 100% that there was no disease, you would probably only need a few pap smears during your lifetime to avoid cervical cancer. This is because cervical cancer takes a long time to develop once the cervical cells start changing. Medicine was able to overcome this problem by recommending that pap smears be performed every year. That way, if early disease was missed in one, or even two years, it was still likely to be picked up before serious changed had occurred. This worked out well to pick up changes early and treat them before they ever became cervical cancer. The number one cancer killer of women decreased dramatically. Deaths from cervical cancer from between 10-22/100,000 women in 1950 to less than 3/100,000 women thirty years later.
Once cervical cancer was under control, the problem of the high rate of false positives for this screening test became more apparent. Yearly screening with a test that has a 20% rate of false positive results meant that many, many, many women underwent evaluation and treatments that were not needed. When the pap smear is abnormal, a colposcopy (examination of the cervix with a microscope) is recommended. Biopsies are usually taken and if abnormal cells are found, more frequent colposcopies or more invasive treatments are recommended.
In the late 1980’s, decades of data and follow up on the performance of pap smears made it clear that yearly pap smears were not necessary to prevent cervical cancer. Doctors were learning that once the cells of the cervix start becoming abnormal, it still takes ten to twenty years for cervical cancer to develop. After evaluation of the natural course of cervical changes, it was clear that pap smears should be performed less frequently. They would still pick up changes in more than enough time to prevent cancer. Recommendations changed; pap smears should be performed every three years in women with normal results.
Most women then ask, “Why shouldn’t I have my pap smear every year, just to be safe?” And most women in the US did continue to have their pap smears every year. And most doctors continued to recommend and do pap smears every year until very recently. Some doctors were even recommending routine pap smears twice yearly! The problem with yearly screening is that about 75% of women will have an abnormal pap smear during their lifetime with yearly screening. Most of these women will go on to have multiple colposcopies and biopsies along with the worry, discomfort and expense associated with the procedure. The large majority of those women will have had only minor changes that will resolve with no treatment except the passage of time. Spacing of the pap smears to every three years would miss many of these benign, self limited changes without missing the serious changes that need evaluation and or treatment.
In the early 2000’s, HPV testing was added to the pap smear for routine screening. Human papilloma virus (HPV) is now known to be the root cause of cervical cancer. If a woman tests HPV negative, she is not at risk for developing cervical cancer over the following ten or maybe twenty years. Current recommendations prefer pap smear and HPV testing every five years for women who have normal results. It is also acceptable to do pap smear screening alone every three years for women with normal results.
Patients should not worry that these screening intervals are not “safe” and that they will be at risk for cervical cancer if they do not get a yearly pap smear. Most cervical cancers are discovered in women who have never had a pap smear. The rest are diagnosed in women who have not had a pap smear in the previous five years.
As always, there are exceptions for women who are on certain medications or who have other infections that suppress their immune system and may make them more susceptible to disease. The best recommendation is always to talk to your doctor. A complete history and appropriate physical exam are the best way to determine the proper testing for each individual person.
For a complete review of current pap smear screening recommendations: