Part 3 of the Cancer 101 Series
Please note: This article appears in both Gyn Cancers Resource Center and the HPV/Dysplasia Resource Center. Soon, I will have a customized version for each site, but at this time some of the links will not work. Thanks for your patience.
by Laura Dolson
As most women are aware by now, the Pap test has saved countless lives by detecting abnormal cells on a woman's cervix (or sometimes vagina) before they have a chance to progress to cancer. The condition that is detected is called dysplasia, which literally means abnormal cell growth. In the female reproductive system, dysplasia can occur on the cervix, vaginal, or vulva - however the vast majority of the time it is on the uterine cervix. It is important to emphasize that dysplasia is NOT cancer, but we can think of it as changes that are "moving towards" cancer or precancerous.
Why the cervix? - Although the tissue structure of most organs is fairly fixed, the cervix is different. The surface of the cervix is roughly divided into two sections: the exocervix (also called the ectocervix) is the part which extends into the vagina and is covered with squamous cells (similar to skin). The endocervix (also called the cervical canal) is the part of the cervix that extends into the uterus, and its surface is made up of columnar cells, which excrete mucous. The odd thing is that over the course of a woman's life, the line between these two areas moves inward, creating a transformation zone, or T-zone (also called the squamous-columnar junction), where this change is taking place. It is this T-zone which is most vulnerable to dysplasia.
Causes - The causes of dysplasia are complex, and not yet fully understood. Although it's very popular right now to throw all the blame on HPV, the fact is that the vast majority of women who are infected with HPV never get dysplasia. So what makes the difference? General health, immune system function, smoking, and nutrition (eating fruits and vegetables and getting adequate amounts of vitamin A and antioxidants seem to have a protective effect) - all these seem to play some part. Research will certainly tell us more in the next few years.
Age at first exposure to HPV may also make a difference - it may be that during the first few years after puberty a young woman's cervix is more vulnerable. In any case, studies have shown a correlation between sexual intercourse before 16 or 18 (depending on the study) and cervical dysplasia. One is tempted to blame exposure to infectious organisms such as HPV, rather than the intercourse itself.
Detection - The Pap test is the major front-line test for dysplasia. During this test, cells are taken from the cervical area and examined under a microscope for abnormalities. All women should get an annual Pap test, beginning at age 18 or when becoming sexually active, whichever comes first. Do not think that being young is a protection from dysplasia and cervical cancer - this is not the case!
Categories of Dysplasia - There are two different systems for classifying dysplasia. There are some differences between them, although what they are describing is similar. Let's walk through them:
The Bethesda, or SIL (squamous intraepithelial lesion) System looks only at individual cells, generally from a Pap test, and classifies them according to the degree of cell abnormality. These break down into:
- ASCUS (atypical squamous cells of undetermined significance) means the cells aren't quite right, but they aren't clearly dysplastic, either. This can be caused by a lot of different factors, including hormonal changes, yeast or other infections, medications, or other sources of inflammation. HPV testing is sometimes done at this point to help decide whether to wait and do another Pap in a few months or do further testing sooner.
- AGUS or AGCUS (atypical glandular cells of undetermined significance) is a finding of atypical glandular cells. This is less common, but since a different type of cancer (adenocarcinoma) develops from glandular (mainly the columnar) cells, this is usually followed up right away with more testing. Adenocarcinoma often doesn't have the extended precancerous phase that squamous cell carcinoma does.
- LSIL - low grade squamous intraepithelial lesion - this is also called "mild dysplasia", however, the true degree and extent of the dysplasia can only be determined upon further evaluation of the cervix itself. Since most LSIL "regresses" - that is, returns to normal without treatment, a woman with LSIL may be advised to return for another Pap test in a few months. Some physicians are more cautious and do more careful follow-up at this point, however.
- HSIL - high grade squamous intraepithelial lesion - this type of Pap result will always be evaluated further and treated, as it detects cell changes that have progressed beyond the mild stage.
CIN system - The other major system of classifying dysplasia is called the CIN system, for cervical intraepithelial neoplasia. There are corresponding classifications for vaginal and vulvar dysplasia called VAIN and VIN. This system of classification is based both on the degree of dysplasia in the individual cells (like SIL) and how far below the surface (epithelium) of the cervix the dysplasia goes. To determine the level of CIN, a small piece of tissue is usually obtained via biopsy. Although it's not uncommon to see Pap tests interpreted in terms of CIN, in my observation there is a trends towards using the SIL system for the cellular changes found in a Pap test, and then using CIN to describe the depth of the dysplasia found in a biopsy.
- CIN I - corresponds to mild dysplasia or LSIL. Additionally, the abnormal cells are only on the very surface of the cervix. As stated under SIL, most of these will regress back to normal over time. About 11% will progress to CIN 3. Only a very small percentage of CIN I leads to cancer.
- CIN 2 - corresponds to moderate dysplasia or HSIL. About half of the thickness of the epithelium is abnormal (dysplastic). Left alone, about 43% of CIN 2 will regress back to normal, and 20% will progress to CIN 3.
- CIN 3 - corresponds to severe dysplasia or HSIL. All or almost all of the epithelium is dysplastic. Although some CIN 3 will spontaneously regress, this is almost always treated since the next step is cancer. This is sometimes also referred to as carcinoma in situ (CIS).
Cancer - by definition, when dysplasia invades the basement membrane, which is the layer of cells under the epithelium, it has become malignant (cancerous).
Another term creeping more into Pap smear reports is koilocytosis, which refers to a type of cell change commonly caused by HPV. Koilocytotic changes are not cancerous or precancerous, but warrant monitoring. They are often accompanied by dysplasia.
Next >Dysplasia Eval and Treatment
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