The Importance of Pap Testing
Edition: April 2003 - Vol 11 Number 04
The traditional Pap test – also referred to as a Pap smear – is an essential tool in any doctor’s office. A means for collecting cells from the cervix, the test enables physicians to examine the cells for abnormal changes. The earlier any changes are detected, the greater the odds for preventing – or successfully treating – cervical cancer.
The clinician or physician uses a wooden scraper or small cervical brush to remove a sample of cells from the female patient’s cervix. He or she then either places the specimen on a glass slide and preserves it with a fixative, or rinses it in a vial of fixative. A lab then examines the sample.
Of the 55 million Pap tests performed annually in the United States, 6 percent – or 3.5 million – generate abnormal results, according to the National Cancer Institute (NCI).
Responding to Abnormal Tests
When Pap test results are abnormal, the physician initially may repeat the test to determine if follow-up treatment is needed. Sometimes, cell changes disappear without treatment. Women who are near or past menopause may incur cell changes as a result of low hormone levels. In such cases, the physician may prescribe an estrogen cream.
In more extreme cases, the physician may follow up either with a colposcopy and biopsy, or an endocervical curettage (scraping cells from inside the endocervical canal).
When lab results determine that abnormal cells are a high risk for cancer, any of the following treatment options may be necessary, according to the NCI:
• LEEP (Loop electrosurgical excision procedure). Employs an electrical current passed through a thin wire loop.
• Cryotherapy. Freezes abnormal tissue to destroy it.
• Laser therapy. Destroys or removes abnormal cells.
• Conization. Removes a cone-shaped piece of tissue using a knife, laser or LEEP.
Pap tests, while critical for early cancer detection, once in a while may generate false-positive or false-negative results. A false-positive result is one where the patient is told she has abnormal cells when she actually has normal cells. With false-negative results, the patient is told her cells are normal when, in fact, they are abnormal. This can delay diagnosis or treatment of cervical cancer.
In 1996, the National Institutes of Health (NIH) organized the Consensus Development Conference on Cervical Cancer, which determined that about half of false-negative Pap test results are due to inadequate specimen collection, while the other half occur because of a failure to interpret the specimen accurately. Over the years, advances in Pap test technology have responded to the need for more precise collection and analysis methods.
During a Pap test, only a portion of a patient’s sample is transferred to the slide, according to Cytyc Corp., based in Boxborough, Mass. Up to 80 percent is discarded along with the sampling device. In 1996, Cytyc received FDA approval to make the following claims about its ThinPrep 2000 system:
• ThinPrep 2000 is significantly more effective than conventional Pap smears for detection of LSIL and more severe lesions.
• ThinPrep 2000 offers an improved specimen quality over that of conventional Pap smears.
The ThinPrep system only examines about 70,000 cervical cells compared to a conventional Pap smear, which collects up to 300,000 cells. But when so many cells are on a slide, they often overlap or become obscured by blood, mucous or inflammation, according to Cytyc. The ThinPrep sample is not smeared onto a slide, thereby avoiding the problem of clumping cells together. Further, a greater portion of the sample can be preserved.
How it Works
The ThinPrep sample is collected with a brush-like spatula device. Once the cervical cells are collected, the sampling device is rinsed in a ThinPrep vial containing the PreservCyt transport medium. The sampling device is then discarded and the vial is sent to the lab for slide preparation.
Before the cellular material is transferred to a slide, the vial is placed in a ThinPrep 2000 Processor, which breaks up any blood, mucous or non-diagnostic debris. The sample is then mixed well.
The processor generates a negative pressure pulse, which draws fluid through a TransCyt Filter. The filter collects a thin layer of diagnostic cellular material. The processor continuously monitors the rate of flow through the TransCyt Filter during the collection process, ensuring that the sample isn’t too thin or too dense, according to Cytyc. Finally, the processed cellular material is affixed to a glass slide for examination.
Obtaining the best cervical cell sample is critical to reduce the rate of false-negative Pap tests. The Papette, made by Orange, Conn.-based Wallach Surgical Devices Inc., is a one-step collection device designed for use with either conventional Pap tests or the ThinPrep system. The design of bristles in varying lengths reportedly makes the Papette a gentler collection device than traditional brushes and scrapers.
Employing a simple rotating motion, the clinician can use the Papette to collect a full range of endocervical and ectocervical cells – including the transformation zone – with less tissue trauma, according to Wallach. This translates to less bleeding for the patient.
Wallach reports the following features of the Papette:
• Higher overall cell yield for improved Pap test accuracy.
• Reduced false-negative testing.
• Faster conclusive results.
Pap testing in itself is not new, but much of the technology available is. Testing has helped reduce the number of cervical cancer deaths from 35,000 a year to less than 5,000 over the last half-century, according to Quest Diagnostics in Teterboro, N.J. It goes without saying that your customers need the best tools available to help their patients avoid cervical cancer.
Study Identifies cancer-inducing viruses
A report in the New England Journal of Medicine (Feb. 6, 2003) describes a recent study in which researchers were able to determine that 15 types of Human Papillomaviruses (HPV) are associated with a higher risk for cervical cancer. Another three types of HPV have been classified as likely to be a high risk factor. Women with one of four types of HPV (HPV 16, 59, 33 and 18) have a 200-fold increased risk for cervical cancer compared with women with no HPV, according to the study.
HPVs – a group of over 100 viruses – range in seriousness from causing common warts to being associated with cervical cancer. More than a dozen sexually transmitted HPVs are linked to cervical cancer. Although HPV infection is common, few women with untreated HPV infections actually develop cervical cancer.
HPV infection more commonly develops among women in their late teens and twenties. It is spread mainly through sexual contact (nonsexual transmission of HPVs is rare), and the risk increases with the number of sexual partners, according to the National Cancer Institute. Women infected with HIV are at higher risk for infection with HPV.
Knowing which HVP types lead to cancer can help doctors determine which types to include in diagnostic testing and use in screening programs, according to Dr. Nubia Munoz, a researcher at the International Agency for Research on Cancer, as reported by Reuters Health. This information can also help decide which HPV types to include in vaccines, notes Munoz.