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Pap smears are like routine car service. You’re not exactly sure what's being checked or why, but you know you should get them. Even well-informed women who know that a Pap test is primarily a screen for cervical cancer are still unsure as to whether it also checks for sexually transmitted infections, ovarian cancer, uterine cancer as well as general "gynecologic wellness." So, what exactly is a Pap test?

In 1928, after spending months observing his own wife’s cervical cells under a microscope, Dr. George Papanicolaou invented the Pap smear as a method to detect cervical cancer. His discovery has withstood the test of time. Dr. Papanicolaou can be credited with the fact that cervical cancer is now a rare cause of death in the U.S. despite the fact that it remains the leading cause of death in countries where Pap smears are not routinely performed. (Though it seems Mary Papanicolaou should get at least some of the credit for submitting to countless exams to support her husband’s research!)

Most women are familiar with the basic process: A speculum is inserted into the vagina in order to sample cells from the surface and canal of the cervix. The cells are then sent to a lab where they are checked for abnormal cell growth, also known as dysplasia or cervical intraepithelial neoplasia (CIN).

Every year, more than 3.5 million women receive that stomach-dropping notification: "Your Pap smear is abnormal." But even if dysplasia is detected, the chance of a real cervical cancer is relatively small. Out of that 3.5 million, only 13,000 are likely to have a true cancer. The rest will ultimately find out that there's nothing wrong with their cervix, or they have a dysplasia which can be easily treated, or more likely, that will go away on its own.

Next: What type of HPV you should worry about, and what type is really no big deal
If the Pap smear results are abnormal, the next step usually involves colposcopy, which is nothing more than a microscopic examination of the cervix done in the office. While a Pap smear samples random cells, colposcopy allows the gynecologist to inspect the surface of the cervix under magnification so that the area where the abnormality is located can be targeted and biopsied. The small sample of tissue removed is then sent to a pathologist who will report one of the following:

Normal tissue
Frequently, the cervical cells are found to be normal, which indicates that the cells reverted back to a normal growth pattern. Occasionally, abnormal cells are still present, but are located high up in the cervical canal, beyond the view of the colposcope, which is why a follow-up short interval Pap smear is always the next step.

HPV changes
Human Papilloma Virus (HPV) is responsible for dysplasia and cervical cancers. Sometimes cellular changes indicate the presence of the virus, but there are still no actual pre-cancerous cells.

CIN I (mild dysplasia or low grade squamous intraepithelial lesions)
CIN II (moderate dysplasia or high grade squamous intraepithelial lesions)
CIN III (severe dysplasia, or high grade squamous intraepithelial lesions, also known as carcinoma in situ)

Invasive Cancer (true cancer which has infiltrated surrounding tissue and has the ability to spread)

Dysplasia is the result of infection with the sexually-transmitted HPV virus. When discovering you have been exposed to HPV, keep in mind that this could have occurred years before dysplasia shows up, and may have nothing to do with your current partner.

This is an important distinction: Almost all women with cancer have HPV, but most women with HPV never develop dysplasia or cancer. HPV is extremely common; some studies show that it is present in the cervixes of almost 80% of sexually active women. There are over 100 subtypes of HPV, but it is the high-risk subtypes that are most likely to progress to cancer. This is why your gynecologist may diagnose you with HPV and then reassure you that it's not a big deal and you really shouldn't have to worry about it.

Next: Who needs pap smears and when
For years, women were told that they needed to get a Pap every year, but now that the necessary annual ritual is no longer deemed as necessary, many women are confused.

The American College of Gynecologists has issued new, very specific guidelines, which are as follows:
  • Pap tests should begin at age 21.
  • From 21-30, it is fine to get a Pap every two years instead of every year as long as you have had three normal Pap tests in a row and are considered low risk, meaning you have never had moderate or severe dysplasia, cervical cancer, HIV or have a severe medical illness that compromises your immune system.
  • After age 30, every three years is fine, but only for women who are low risk.
  • After age 70, you can cross scheduling Pap smears off your "to-do" list as long as you have had a normal test for at least 10 years.
There are two main reasons for this change. Most abnormal Paps have minimal potential for progression to cancer. This is particularly true for young women. In the event that a persistent dysplasia is present, the transition from pre-cancerous cells to a true cancer takes not weeks or months, but years.

This doesn't mean that you only need to see your gynecologist once every three years. Even if you're not due for a Pap, you still need to have a breast exam, STD screen, and a pelvic exam to check your uterus and ovaries. And even if you don’t need to have cells sampled from the cervix, your gynecologist will still want to do a basic exam to make sure the cervix and vagina look healthy.

It's important to keep in mind that Pap smears don’t detect 100% of abnormalities. I once biopsied a suspicious growth on a patient's cervix that turned out to be an early cancer. Her Pap smear the year before was read as normal, and had she not come in for her annual exam, I would not have had the opportunity to detect the growth.

Lauren Streicher, M.D., is an Assistant Clinical Professor of Obstetrics and Gynecology at the Feinberg School of Medicine at Northwestern University in Chicago.

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