Michelle Collins The Papanicolaou (Pap) test is a screening test for cervical cancer that involves collection of exfoliated cervical cells for cytologic staining and examination. Among the 30 million Pap tests performed annually in the United States, approximately 1.4 million (2.1%) reveal cytologic abnormalities requiring follow-up.1 Cervical cancer affects approximately 12,000 U.S. women annually, with 4000 women dying from cervical cancer every year.2 Cervical cancer mortality has decreased by 70% since the introduction of the Pap test 50 years ago; however, health disparity research has revealed that poor women, and particular ethnic minorities, have a higher incidence of cervical cancer mortality within the United States, with rates higher in African-American and Hispanic women than in white women.3 Women immigrating to the United States from countries where cervical cytology screening is not routinely practiced are a group at particularly high risk.4 It is well known that particular strains of human papillomavirus (HPV) are involved in the etiology of cervical cancer. Papillomaviruses are small, double-stranded DNA viruses. Among the more than 100 types of HPV, 30 to 40 are genital subtypes; approximately 13 of those are high-risk types, particularly types 16 and 18, which are implicated as the cause of approximately 70% of all cervical cancers. HPV-16 accounts for approximately 50% of cervical cancers worldwide. Low-risk HPV subtypes, such as HPV-6 and HPV-11, are associated with genital warts and are not implicated in the etiology of malignant cervical disease.5 HPV is the most common sexually transmitted infection in the United States, with at least 50% of sexually active persons becoming infected with at least one type of urogenital HPV during their lifetime; some estimates extend that to 80%. Although it is known that the presence of HPV is a necessary component for the development of cervical cancer, only a very small proportion of those women who are infected with HPV actually develop cervical cancer, which suggests that cervical cancer is a multifactorial phenomenon. It is the persistence of the HPV infection that is thought to be the impetus for precancerous and cancerous lesions.6 Most HPV lesions resolve spontaneously, particularly in young women. This information, the result of research tracking women with HPV for several successive years, has led to the significant revision of screening and management guidelines for women younger than age 24. The development of cervical cancer is multifactorial. Some identified associated factors include older age, infection with particular high-risk HPV types, vaginal pH changes, hormonal changes, cellular trauma, long-term use of combined hormonal contraception, young age at coitarche, multiparity, history of sexually transmitted infections, having a sexual partner with a history of a sexually transmitted infection, having a higher number of lifetime sexual partners (defined as more than 5), younger age at first pregnancy, and cigarette smoking.7 HPV contains genes that encode proteins with particular functions in the life cycle of the virus. Among high-risk HPV types, the role of E5, E6, and E7 proteins is unique, allowing high-risk types of HPV to take control of an infected host cell for its own replication and survival. A normal host cell contains two important tumor suppressor genes (p53 and pRb) that act as the guardians of the cell. Among high-risk HPV types, such as HPV-16, E6 and E7 proteins interfere with the p53 and pRb host cell tumor suppressor genes, disrupting the normal cell life cycle. In a normal nonreplicating cell, pRb is bound to another protein, E2F, which is required for DNA replication. When HPV viral protein E7 displaces the connection between pRb and E2F, the usual control that pRb exerts over cell replication is disabled. Unbound E2F causes a normally nonreplicating cell to begin the complex sequence of cell replication necessary for the survival and reproduction of HPV. Usually, if pRb is dysfunctional, the other guardian of the cell, p53, recognizes this dysfunction and initiates a mechanism that suspends the cell cycle processes to repair the damage. Normally, when p53 recognizes that the damage is not reparable, it triggers apoptosis (programmed cell death), preventing the damaged cell from future replication. However, HPV also disables p53, thereby allowing damaged cells to escape death and HPV to thrive. This aberrant replication process increases susceptibility to gene mutation. An unstable genome gives rise to carcinogenesis.8,9 HPV enters the body during vaginal, anal, or oral sexual contact, or by skin-to-skin transmission through intimate sexual contact. The virus passes through the cervical epithelium to the basal cell layer, where it enters the normally replicating basal cell and exploits the replicating machinery of the basal cell to establish itself and then begins to reproduce insidiously. It then accompanies the host cell through natural epithelial cell maturation until it is detectable in the normally nonreplicating suprabasal cells and surface epithelium.10 After initial infection, HPV may exist as a latent infection for a period of months. Then it enters its productive phase, during which the virus produces a protective capsule that allows it to survive attached to superficial and exfoliated squamous cells. This protective capsule makes HPV highly infectious and sexually transmittable. Persistent HPV infection, combined with other cofactors, gives rise to cervical dysplasia, also described as cervical intraepithelial neoplasia (CIN). Low-grade lesions detected by Pap test and confirmed by cervical biopsy have a fairly high regression rate and frequently resolve spontaneously; the probability of regression of CIN 1 is approximately 70% to 80% in adult women, and greater than 90% in adolescents and young women.11 However, high-grade lesions detected by Pap tests and confirmed by cervical biopsy are more likely than CIN 1 lesions to progress to cervical cancer than to regress, particularly for lesions that are CIN 3 as compared with those that are CIN 2.12 In women who are immunocompromised, there is an even greater likelihood that cervical disease will ultimately progress. Although frank cervical cancer may appear as a visible cervical lesion on the cervix, most cervical lesions detected as Pap test abnormalities are not visible by routine speculum and pelvic examination. Two techniques are currently available for Pap test specimen collection. The traditional Pap test involves collection of endocervical cells with a cytobrush or cotton swab, and collection of ectocervical cells with a wooden or plastic spatula. A slide is prepared, and fixative is applied immediately after specimen collection. A more recent technology for Pap test specimen collection and processing uses a liquid-based medium (SurePath, ThinPrep). The examiner uses either a plastic spatula and endocervical brush, or a cytobroom, for cell collection and then places the specimen in the liquid medium. The laboratory centrifuges the specimen, allowing the separation of cervical cells from blood, mucus, and cellular debris. When liquid-based cytology is used in the collection of a Pap test specimen, additional testing for gonorrhea, chlamydia, and HPV can be performed from the same specimen. Additional testing is not able to be done with the slide method of Pap testing. HPV DNA testing has been approved by the U.S. Food and Drug Administration (FDA) as an adjunct to Pap testing when atypical squamous cells of undetermined significance (ASCUS) are detected. The FDA has also approved HPV DNA testing as a screening test for women older than 30 years as an adjunct to the Pap test. This age limitation is based on the concern that the high prevalence of inconsequential, transient HPV infections among women younger than 30 years would lead to an abundance of positive HPV results, resulting in unnecessary procedures and psychosocial concerns. HPV infection among women 18 to 25 years is more commonly transient and appears to frequently resolve spontaneously or to become undetectable within a period of 2 years.13 Women older than 30 with a normal Pap test result and negative high-risk type HPV DNA test result can extend Pap test screening intervals to every 5 years rather than annually.12 The accuracy of Pap test screening depends, in large part, on proper specimen collection technique. Optimally, a Pap specimen should not be obtained during menses, or within 24 to 48 hours of having had intercourse or having used topical medications for vaginal infections. Health care providers should be aware that the Pap test sample should be obtained from the transformation zone of the cervix. The normal ectocervix (external surface of the cervix) is covered by stratified squamous epithelium. The endocervix (internal surface of the cervix) contains mucus-secreting columnar epithelium. The normal physiologic process of metaplasia transforms columnar epithelium into squamous epithelium, with the border between the columnar and squamous epithelium known as the squamocolumnar junction. The region of the cervix where columnar epithelium transforms into modified squamous epithelium is aptly named the transformation zone. The location of the squamocolumnar junction and the transformation zone varies according to a woman’s age and hormonal influences. It may be located on the ectocervix, at the cervical os, or just inside the endocervix.9,12 In 2012, existing consensus guidelines for the management of women with cytologic abnormalities, based on the Bethesda system of classification for the reporting of abnormal cervical cytologic findings, were revised (Box 166-1). ASCUS or low-grade squamous intraepithelial lesion (LSIL) is classified as low-grade lesions. High-grade squamous intraepithelial lesion (HSIL) and carcinoma in situ (CIS) are classified as high-grade lesions. The Pap result “atypical squamous cells, cannot rule out high grade” (ASC-H) is associated with high-grade lesions. High-grade lesions represent precursor lesions for the development of squamous cell carcinoma of the cervix. Atypical glandular cells, which are less frequently reported, may represent a precursor lesion for adenocarcinoma of the cervix.
Pap Test Abnormalities
Definition and Epidemiology
Pathophysiology
Clinical Presentation and Physical Examination
Diagnostics: Cervical Cancer Screening
Management
Pap Test Abnormalities
Chapter 166
