Pap Test Health Article

Description

The Pap test is an extremely cost-effective and beneficial test able to detect about 95% of cervical cancer. According to a report published May 16, 2000 in the Annals of Internal Medicine, the widespread use of this diagnostic procedure decreased the number of cervical cancers in the United Sates from 14.2 per 100,000 in 1973, to 7.8 per 100,000 in 1994. However, the disease still ranks as the ninth-leading cause of cancer deaths in U.S. women.

During the pelvic examination, an instrument called a speculum is inserted into the vagina to open it. A spatula, (Ayre spatula) that is flat at one end and curved at the other so that its contour complements the ectocervix is used to collect the sample. The spatula is firmly rotated using a circular motion to scrape the cells off the ecto-cervix. The flat end can be used to pick up cells which have exfoliated from the rear of the vagina. This procedure, called vaginal pool sampling, is recommended for women in menopause and if signs of inflammation are seen. A tiny brush, pointed spatula, or cotton-tipped swab is used to collect cells from the endocervix. These samples can be mixed and spread evenly on a single glass slide, or a slide or slide section can be used for each. The slide should be dipped in 95% alcohol or sprayed with fixative immediately. Though some women find the procedure uncomfortable, it is usually painless and only takes five to 10 minutes.

A new technique called the Thin Prep is being used by some physicians because it is purported to reduce the false negative rate caused by inadequate smear preparation. For the Thin Prep, the sample is placed in a vial containing a preservative solution. The vial is labeled and sent to the laboratory where a processing instrument disrupts the blood cells and mucus and spreads the decontaminated sample in a thin layer over the slide. Unlike the classical procedure, cells are not left on the collection device. This results in a greater yield of epithelial cells to examine. The staining detail is easier to evaluate because the epithelial cells are not obscured by blood cells or mucus.

Smears are stained with the Papanicolaou stain when they reach the lab. The Pap stain begins with rehydrating the cells in water. The cells are stained with Gill hematoxylin, then dehydrated with 95% ethanol. They are stained with OG-6 followed by EA-65, then fully dehydrated with absolute ethanol. In the last step, they are cleared with xylol, and a coverglass is applied. The entire smear is examined under a microscope. In addition to detecting and classifying abnormalities within the squamous epithelium and glandular epithelium, the smears are also examined for the presence of inflammatory cells (polymorphonuclear white cells, lymphocytes, histiocytes), normal vaginal flora (Lactobacilli), coccobacilli (indicative of vaginal infection), trichomonads (vaginal parasites), yeast, and cytopathic effects of viruses in the epithelial cells.

Squamous epithelial cells from the cervix are evaluated for abnormal intracellular changes that indicate a risk of cancerous transformation. Two systems of classification are widely employed, the CIN (Richart) and Bethesda systems. Both describe a progression of cells from normal to low risk, then to high risk, then to malignant

cells. The CIN system uses the term, cervical intraepithelial neoplasia (CIN) to describe premalignant cells. CIN-I is characterized by mild cellular abnormalities (mild dysplasia), CIN-II moderate dysplasia, and CIN-III severe dysplasia. CIN-III includes the presence of immature cells with cancerous features that have not yet invaded the surrounding connective tissue. This is called carcinoma in situ. When such cells are found beyond the transformation zone (within the underlying stroma), the lesion is classified as invasive cancer (squamous carcinoma). The CIN classification system classifies cells that are most likely benign (called squamous atypica) and low-risk precancerous cells in the category of CIN-I. In 1989, the Bethesda system was introduced in order to more clearly define the difference between mild dysplasia that is likely to be benign and that which is pre-cancerous. The former comprise a group called ASCUS which stands for atypical squamous cells of undetermined significance. This distinguishes cells that are often reactive from those of the next group, low-grade intraepithelial neoplasia (LSIL) that show precancerous changes, but are at a low risk of transforming into cancerous cells. ASCUS is reserved for cells that cannot be conclusively called benign. Classification of a smear as ASCUS is based upon judgement and depends upon the quality of the smear and the numbers and appearance of atypical cells present. A pap test in which ASCUS is found should be repeated in three to four months, and if ASCUS is detected the second time, the patient should be evaluated by colposcopy and biopsy. Between 19% and 57% of these patients will be reclassified as SIL on the

basis of biopsy. The LSIL category is the counterpart of the CIN-I category. The final category of the Bethesda system is high-grade intraepithelial neoplasia (HSIL) which comprises both CIN-II and CIN-III groups including carcinoma in situ. Beyond HSIL, the lesion is classified as an invasive squamous cell carcinoma.

In general, cervical cells are classified as ASCUS if the nuclear enlargement is no greater than three-fold the size of the nucleus of a normal intermediate squamous cell, or there is mild hyperchromasia (increased chromatin staining). LSIL cells are superficial or intermediate squamous cells that display a nucleus that is at least three-fold larger than the normal intermediate squamous cell. There is moderate variation in the size and shape of the nucleus. Nuclear hyperchromasia is present either as uniformly granular or smudged chromatin staining. In addition, cells that are associated with infection by HPV have a cytoplasm with hollowed-out cavities. About 80% of cervical cancers are associated with HPV infection. Therefore, these cells, called koilocytes, are classified as LSIL provided that some nuclear abnormality or binucleation is present. HSIL cells are immature squamous cells (smaller cells) with a three-fold or greater nuclear enlargement, an increased nuclear to cytoplasm ratio, severe hyperchromasia with irregular chromatin and nuclear membrane contour. They are usually seen in streaming rows or groups of attached cells.