THE PAP SMEAR
The Pap smear was introduced in 1943 by George Papanicolaou and Herbert Traut, researchers at Cornell University’s New York Hospital. Since then, cervical cancer in the U.S. has fallen by almost 80%. Even today, women who get regular Pap smears are only about a third or a tenth as likely to get cervical cancer as those who don’t.
TAKING A PAP SMEAR
The idea of the Pap smear is a simple one. At the time of a pelvic examination with a speculum, a flat piece of wood or plastic is used to wipe the cervix, which is the part of the uterus or womb that is visible at the top of the vagina. Also, a small brush is passed into the opening of the cervix. This material, which contains cells, is then smeared onto a glass slide. This is quite like the high school science exercise in which students wipe the inside of their cheek, smear it on a microscope slide, and examine the cells under a microscope.
Pap smears taken in the doctor’s office are taken to the lab where they are stained and examined microscopically. This is done by a cytotechnologist (“cyto” means “cell”) under the supervision of a pathologist. A pathologist is a doctor who specializes in examining tissues and organs of the body. In the old TV show Quincy, Jack Klugman played the lead character who was a pathologist.
PAP SMEAR RESULTS
From the appearance of the cells, the cytotechnologist and pathologist try to determine the status of the cervix. If the cells look like those that typically fall off of a normal, healthy cervix, the pap smear is read as negative. Sometimes the cells look they have come from a cervix that is inflamed or micro-organisms are seen that suggest a vaginal infection. But the most important part of the Pap smear is determining whether the cells seen may have come from a cervix which is dysplastic. Cervical dysplasia is considered a pre-cancer and is graded as mild, moderate or severe or, alternatively, as low-grade or high-grade.
Although it may not sound it, pre-cancer is not a life-threatening condition. Pre-cancer never killed anyone. But pre-cancers have a tendency to become cancerous. This can take anywhere from months to years, with moderate and severe or high-grade dysplasias having the highest tendency to persist or progress.
One problem with Pap smears which has been known for a long time is that they are not very sensitive. That is, if a cervical dysplasia is present but the abnormal cells don’t happen to make it to the slide, the Pap smear will be falsely negative. On the other hand, if abnormal cells are seen, the likelihood of a false result is obviously small. For this reason, the proper management of a Pap smear showing dysplasia is not to just get another Pap. Likewise, when dysplasia is diagnosed and treated, more frequent Pap smears, at least for a while, are commonly done.
The reason why Pap smears are so valuable, even though they miss an abnormality 10-25% of the time no matter how they’re done or who reads them, is that dysplasias take time to progress. It can take up to five years, sometimes more, for a mild dysplasia to progress to the earliest form of cancer. So getting a Pap smear every year greatly reduces the chance that this could be missed, while getting Pap smears only occasionally increases this risk.
There is one kind of abnormality reported on Pap smears that creates confusion and aggravation for both women and their doctors and this is atypia or atypical squamous cells of uncertain significance, ASCUS for short. What this means is that some of the cells seen, while not appearing abnormal enough to suggest dysplasia, don’t look entirely normal either. Sometimes this can be due to vaginal infections, lack of estrogen in breastfeeding or menopausal women, or other causes of irritation of the cervix. But sometimes when the Pap reports ASCUS there is actually a dysplasia. The best course of action in these circumstances will vary with the situation.
NEW PAP SMEAR TECHNOLOGIES
A variety of innovations have been introduced in effort to improve the usefulness of the Pap smear.
- Liquid-based Pap smears: these involve placing the collected cells into a container of liquid. The cells are then later spread out on a glass slide for microscopic examination. These methods improve the detection of cervical dysplasia, particularly high-grade lesions and early cancers, but are more expensive and may not offer much benefit for women who have had good medical care.
- Computerized or computer-assisted reading of Pap smears: the idea here is either to identify the Pap smears most likely to be abnormal before examination by human beings or to double-check Paps that have already been read. They can also be quite expensive. One of them costs $33,781 for every additional abnormal Pap smear identified by the computer, as compared to $1,065 for simply having a human being double-check the Pap smear. [JAMA 1998;279:235-7]
- Testing for DNA from the Human Papilloma Virus (HPV): this is the virus that causes genital warts. Because cervical dysplasias and cervical cancers are closely linked to thus virus, and especially to “high-risk” varieties of it, testing for it can help determine the chance that an abnormality, particularly something like ASCUS, is something to worry about. This testing can often be done directly off the Pap smear. Often the test adds little, though, since a persistently abnormal Pap smear even with a “low risk” HPV test result, is not reassuring to most women.
The important thing to keep in mind with all of these technologies is that in medicine, as in the rest of life, what is “new and improved” is not necessarily better. Although companies that sell these products have tried very hard in part by scary advertising to get women to insist on them, the truth is that their usefulness will vary with the situation. Until scientific evidence shows how best they can be used and cost-benefit considerations become more clear, current standards of medical practice do not indicate their routine use.
An interesting aspect of innovations in Pap smear technologies is that, in the past, two slides, rather than one, were usually prepared at the time of a pelvic exam. Managed care medicine effectively forced a change to a single slide in order to save money. But it stands to reason that the more material that is sent to the pathologist, the more likely it is that dysplastic cells will be found. None of the new, more expensive Pap smear technologies have been shown to be better than simply sending two or three or four or five slides to the lab!
WOMEN WHO HAVE HAD A HYSTERECTOMY
Women who have had a hysterectomy no longer have a cervix. These women do not need annual Pap smears if their hysterectomy was done for non-cancer-related reasons. Pap smears every 2, 3 or 4 years may still be advisable, though. When Pap smears are done in women without a uterus, the tissues at the top of the vagina are wiped and then transferred to the slide. Although unusual, vaginal dysplasia can occur and may be more likely in women who have had cervical dysplasia or cervical cancer in the past.
RELATED TOPICS: Cervical Dysplasia, Pelvic Examination