The Value of the Pap Smear

December 14, 2007

The Pap smear, described by Dr. Papanicolaou more than fifty years ago, was easily the single biggest leap forward in preventative medicine for women. Cervical cancer, or cancer of the mouth of the womb (cervix), killed many women because by the time it was diagnosed it was already too far spread to be halted.

This cancer is a microscopic disease; it reaches the dangerous point where it can spread elusively while still only detectable under a microscope. Before the Pap smear, only a lesion visible with the naked eye or felt with an examination was suspect, and of course by that time it was too late.

The Pap smear changed all of that.

Advancing With The Pap

A gentle scraping of the cervix with something as simple as a wooden tongue depressor which was then smeared on a slide offered a look at this environment right in its microscopic back yard. For the first time a diagnosis of "pre-malignancy" could be made and acted upon before mortal danger developed. Hysterectomy afforded women a normal lifespan when such pre-malignancies were picked up by the Pap.

But the Pap was not the perfect answer, because there were too many young women who planned on children.

Twenty years after the Pap was introduced, another test revolutionized the way we diagnose and treat cervical cancer and pre-cancer. A device called a colposcope, nothing more than a microscope on a stick, was used to look at the area from which the Pap smear is retrieved. The science of "colposcopy," a procedure done right in the doctor's office, became the next logical step in investigating an abnormal Pap. It became known that looking at the cervix through powerful lenses demonstrated for the doctor certain irregularities in the "terrain" of the cervix if there were pre-cancerous changes. These characteristic findings could then tip a doctor off as to where the best places to take small biopsies were.

Enter the pathologist

Better than a Pap, which is a disorganized smear of loose cells on a slide cluttered with mucus, inflammatory debris, or menstrual blood, the colposcopist's small biopsy rendered to the pathologist an actual small piece of tissue, submitted the way it actually sat in patient's cervix. Now important information like the severity of the lesion and the depth of invasion could be ascertained. Armed with the Pap smear and colposcopy, gynecologists are now armed with tools that can treat pre-cancerous lesions with more conservative means than hysterectomy. Full child-bearing potential could be preserved while eliminating lesions earlier with simpler methods like freezing, laser, or LEEP (electrical wire excision).

The Human Papilloma Virus (HPV) seems to be a causative agent for cervical cancer and cervical pre-cancer (which we call "dysplasia"). There are certain subtypes of HPV, some only causing vaginal warts, but others which lead down the cancer road. Some women get infected with the different subtypes at the same time, meaning any warts should invite colposcopy.

With the advent of Pap smears and colposcopy, invasive cervical cancer has become a rarity in private practice. But we gynecologists have a confession to make: The Pap is actually a pretty crumby test.

It's value is not that it's all that accurate, but that it makes a good screen. In other words, it may miss a lesion, but if a woman gets routine Paps over and over, sooner or later an abnormality will show up if it's there. (The scary ones are the patients who disappear for five years and then show up for their Paps.)

So the Pap is not a diagnostic test. It's too inaccurate, sometimes missing from 10-40% of lesions. It is merely a screen whose value lies in its repetition. And once something abnormal shows up, colposcopy rules.

But a Pap is cheap, like a good screen should be. And it's easy, like a good screen should be. And it will come through if there's something wrong¡Vsooner or later, like a good screen. The actual diagnosis is made by the colposcope. And if a woman keeps her GYN appointments and a pre-cancerous lesion were to develop, it can be history before resorting to the drastic surgeries that used to be done before colposcopy came along.

 

The Thin Prep Pap Smear

 

To understand why the Pap smear is not a good diagnostic test requires understanding its physical limitations. It is, after all, merely a smattering of loosely smeared cells on a dry slide, which are subsequently covered with a liquid fixative so that nothing will change until examined by the pathology lab it's sent off to. Many different factors can spoil its tidiness, making the pathologist's job of reading it more difficult.

If there is any type of infection¡Vyeast, bacterial, etc., there may be inflammatory debris and blood mixed in to obscure the true nature of the cells being examined. Inflammation can also make normal cells look abnormal, causing the Pap to be over read as dysplasia. Menstrual blood can literally deluge the cells on the slide, making it impossible to read. 

The bottom line here is that the slide on a regular Pap smear can be over-read as well as under-read. If it's under-read, then a lesion goes undetected until the next routine Pap smear. If it's over-read, patients will be subjected to the more expensive colposcopy unnecessarily.

We gynecologists love the Pap smear, but it's a love-hate relationship, because we know there's got to be a better way. True, we always have colposcopy up our sleeve, but we would rather have a screen that didn't push us that way unless there were true dysplasia to diagnose.

That better way has arrived as the ThinPrep system. It differs from the usual Pap technique in that instead of scraping with a stick and a small brush and smearing on a cold slide, the retrieval is similar but the brush and stick are sunk into a solution which will allow the cells to be culled alone. No longer is inflammatory debris, blood, or dried-out cells on a slide a factor in masking a patient's true cervical status.

All of the recent studies emphasize the significantly greater accuracy of the ThinPrep over the regular Pap. The patient herself will notice no difference in the exam, but her peace of mind will be greater. 

After over fifty years, the Pap smear has finally grown up.

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