• • Starting at age 21 or no more than 3 years after becoming sexually active, women should have a Papanicolaou (Pap) smear on a yearly basis until they have had three consecutive normal tests, after which the screening interval can be increased to every 3 years.
  
• • All women whose test samples show cellular abnormalities, persistent atypical squamous cells, or atypical squamous cells of unclear significance that test positive for high-oncogenic-risk human papillomavirus (HPV) require referral for colposcopy and biopsy.

Cervical cancer is the second most common cancer in women worldwide. An estimated 466,000 new cases of cervical cancer are diagnosed each year, resulting in 231,000 deaths. The majority of these cases occur in countries that have limited or no effective screening programs. In the United States and other developed countries, rates of cervical cancer have markedly diminished over the past 30 years as a result of Pap smear screening. Despite this, more than 10,000 cases of cervical cancer are diagnosed in the United States each year, leading to almost 4000 deaths. Countries that initiate Pap screening experience decreases in cancer rates compared with countries that do not. For example, in the mid-1960s, Finland, Sweden, and Iceland all initiated Pap smear screening whereas Norway did not. In the subsequent 20 years, the incidence of cervical cancer did not change in Norway but dropped 50% in the other countries.

Despite widespread screening in the United States, about 50% of all women with cervical cancer have not had a Pap smear in the preceding 3 years and another 10% have not been screened in the past 5 years. Over 50 million Pap smears are obtained each year in the United States, and 7% (3.5 million) of these are abnormal. A woman who never has a Pap smear has a 3.5% risk for developing cervical cancer; this is reduced to 0.8% with Pap smear screening. Infection with high-oncogenic-risk HPV is found in most, if not all, cervical cancers. Detection of high-oncogenic-risk HPV types from cervical samples is now a part of routine clinical management to identify women with abnormal Pap smears who need further treatment

In 1928 George Papanicolaou initiated the sampling of vaginal cells, speculating that these cells would predict which women would develop cervical cancer. His initial findings were not appreciated by the general medical community, but he persevered and, together with Dr Herbert Traut, published a monograph in 1943 that eventually resulted in Pap smears becoming the standard of care in cervical cancer screening. The procedure they outlined was modified in 1947 by Ayre, who collected cervical cells directly using a wooden spatula.

Although the Pap smear (also called the Pap test) has reduced the incidence of cervical cancer by almost 75%, it is difficult to collect and read a Pap smear in a uniform manner. This lack of uniformity led to widespread confusion about what constituted an abnormal test result. The development of common terminology was essential to standardize the interpretation of this cancer prevention test. In 1988, a workshop was held in Bethesda, Maryland, that provided a general consensus on how to read Pap smears and initial guidelines designed to decrease the variability among laboratories in reporting of results.

A second workshop in 1991 modified these guidelines based on actual practice and clinical experience. The Bethesda 1988 and 1991 guidelines both emphasized delineating squamous intraepithelial lesions—low grade (LSIL) and high grade (HSIL)—from atypical squamous cells of unclear significance (ASC-US) and normal Pap smears.

A decade later, numerous questions about Pap smear interpretation had arisen from clinical practice, necessitating another consensus panel, Bethesda 2001. Some of the issues addressed by this panel included ensuring the adequacy of samples, determining the significance of both atypical squamous cells and atypical glandular cells, and assessing the impact of liquid-based technology on reading of a Pap smear. The Bethesda 2001 consensus panel resulted in the following revisions in the terminology used to report Pap smear results, and in management recommendations for women with abnormal results:

• 1. Significant changes were made in the management of atypical squamous cells. The guidelines retained the ASC-US designation and added the subcategory of “atypical squamous cells favoring HSIL” (ASC-H). ASC-US carries a moderately low incidence of CIN 2 or 3 (10%) and very low incidence of cancer (0.1%), whereas ASC-H is associated with a much higher incidence of CIN 2 or 3.
  
• 2. The Bethesda 2001 guidelines also eliminated the categories of “reactive change Pap smear” and “atypical squamous cells of unclear significance favoring reactive change Pap smear.”
  
• 3. The category of “atypical glandular cells of unclear significance” (AGC-US) was eliminated, primarily to avoid confusion with that of ASC-US. On average 44% of women with AGC-US have a subsequent tissue examination that yields a diagnosis of cervical dysplasia, and cancer is diagnosed in 8%.
  
• 4. The finding of AGC was made more specific in the 2001 guidelines with the inclusion of two categories: “AGC favoring neoplasia” and “adenocarcinoma in situ” (AIS).

In the United States, the Bethesda guidelines are used by the vast majority of laboratories. The standard set of terms currently used for reporting test results is summarized in Table 29–1.

Symptoms & Signs

Few, if any, symptoms or signs usually point to the likelihood that a woman will have an abnormal Pap smear result. This is the underlying justification for performing routine, preventative Pap smear screening. Symptoms when present can include abnormal vaginal bleeding, irregular menses, and weight loss.

Pap Smear Technique & Interpretation

Frequency of Screening

The age at which Pap smear screening should be initiated has led to much debate and, in fact, varies in different locations around the world. In the United States, the most recent recommendation is to screen for the first time 3 years after onset of sexual activity or before age 21, whichever comes first. This is likely a very conservative initiation point, because it appears to take at least 10–20 years for cervical cancer to develop. In some European countries, initial Pap smear screening is performed at age 30.

The optimal screening frequency is also debatable and varies greatly. The initial recommendation that women should undergo annual Pap smear screening was based more on convenience for medical providers and patients than on any scientific data. However, this recommendation is supported by the American College of Obstetricians and Gynecologists (ACOG). The American Cancer Society (ACS) recommends every-other-year screening when using liquid-based cytology (see later discussion). After age 30, the interval between screenings can be increased to 2–3 years. More frequent (ie, annual) Pap smears are recommended for women exposed to diethylstilbestrol (DES), women who are immunocompromised (eg, HIV-infected women), and women with a previous history of stage 2 or 3 cervical intraepithelial neoplasia (CIN).

Although Pap smear screening can be performed on a greater-than-1-year basis, a basic gynecologic examination is a recommended component of a yearly medical checkup. The need for yearly gynecologic examinations is strongly supported by ACOG, particularly for the detection of vaginal, vulvar, uterine, and ovarian cancers. It is also important for women to have prompt repeat Pap smear testing, usually within 3–6 months, for inadequately collected or processed samples. Similarly, follow-up colposcopy for abnormal Pap smear results should also be performed within a 3- to 6-month time interval.

Women who have a hysterectomy for nonmalignant reasons do not need Pap smears. Although vaginal Pap smears can be used to follow women posthysterectomy, vaginal cancers are much less common (0.3 per 100,000 women) than cervical cancer. Furthermore, vaginal intraepithelial neoplasia progresses much more slowly than cervical lesions, and there is a high false-positive rate of Pap smears from vaginal tissue. Generally speaking, women older than 65 years of age can stop undergoing screening if they have had three negative Pap smears in the past 10 years, or if other medical conditions predict a short life expectancy.

Sample Collection

The optimal method of collection is one that obtains samples of endocervical cells. The woman is placed in the lithotomy position, a speculum is inserted, and the cervix is brought into view and effaced so that the os can be clearly visualized. Adequate visualization can sometimes be difficult, because the position of the cervix is highly variable. Once an optimal view of the cervix is achieved, the squamocolumnar junction is sampled. The location of this junction varies between women and also changes during the lifetime of a single woman. Before the onset of sexual maturity, the junction is located far lateral to the os. As the woman enters the reproductive years, the junction shifts medially, and with advancing age, it moves up into the endocervical canal.

The sampling device must collect cells from the area surrounding and extending into the os. The extended-tip spatula and cervical broom are more effective sampling devices than the traditional Ayre spatula. Combining a brush with the spatula is a more effective collection method than spatula alone, as well.

Several studies have been performed using a self-sampling technique to provide cells for cytologic evaluation. Self-sampling devices include self-cervical lavages, swabs, cytobrushes, brooms, and tampons that would be inserted into the vagina as far as possible, rotated or left in place for a short period of time, and then removed. In general, these techniques have shown inferior sensitivity (55–94%) but comparable specificity (>80%) to conventional collection devices. Numerous self-sampling techniques to detect HPV viral DNA have also been tested, and these have compared favorably with provider-obtained cervical samples. These methods include cervical swabs, conical brush, tampons, and urine-based testing. Methods to improve further the accuracy of self-collecting tests, using either multiple sampling devices or the same device on multiple occasions, are in development.

Liquid versus Conventional Pap Smear Technique and Automated Reading

The conventional Pap smear technique consists of obtaining a sample of the cervical transition zone (as outlined earlier), applying the cells to a glass microscope slide, fixing the cells, and then sending the specimen (or “smear”) to a pathology laboratory for interpretation. Among the many difficulties with this technique are low sensitivity (50–75%) for all cervical abnormalities; inability to standardize how many cells are applied to the glass slide; uneven distribution of cells; obscuring of cervical epithelial cells by blood, mucus, or inflammatory immune cells; and incomplete fixation due to inadequate air drying or application of fixative. Liquid-based Pap screening solves many of these problems.

With the liquid-based Pap smear technique, the collected cells are placed in a liquid medium and then read in the same medium, allowing for improved visualization of morphologic characteristics. To date, two liquid-based cytology systems have been cleared by the Food and Drug Administration (FDA): the SurePath system (Tri Path Imaging, Burlington, NC) and the ThinPrep system (Cytyc, Boxborough, MA).

Using the SurePath system, collected fluid is density centrifuged to remove debris, and the remaining cells are allowed to attach to a glass side. This technique has been shown to be equivalent to conventional testing. In the ThinPrep system, the fluid is passed through a filter, which removes debris and creates a thin even layer of cellular material on the slide. Using the ThinPrep system, ASC-US, LSIL, and HSIL were all detected more readily than with a conventional smear. One of the main advantages of liquid-based systems is that they allow for HPV DNA testing on the residual fluid.

Automatic reading devices were invented and are FDA-cleared for quality-control purposes in the repeat evaluation of Pap smear results. Test systems include the PAPNET, which uses a neural network, and AutoPap, which is a computerized high-speed video microscope. The AutoPap system has also been cleared for the primary screening of Pap smears and has generally shown an increased sensitivity for all grades of Pap smear. This system has shown statistically significant improvements on sensitivity for ASC-US and LSIL but not for HSIL compared with technician-read smears.

Interpretation

Adequacy of the sample is paramount in the interpretation of a Pap smear. The Bethesda guidelines recommend that 8000–12,000 squamous cells be obtained for a conventional Pap smear but only 5000 cells for a liquid-based sample. For both sample types, 10 high-powered fields should be read. Cells can be obscured by blood, mucus, and inflammatory cells. If more than 75% of the cells are obscured, the sample is inadequate and a new sample must be tested. If 50–75% of the cells are obscured, the sample is adequate but partially obscured. The presence of endocervical cells (at least 10) is recommended but not required in samples from women younger than 40 years of age but is required from women older than 40.