Value of Cervical Cytology: Cervical Dysplasia & HPV
WHEC Practice Bulletin and Clinical Management Guidelines for healthcare providers. Educational grant provided by Women's Health and Education Center (WHEC).
Dysplasia or cervical intraepithelial neoplasia (CIN) means disordered growth and development of the epithelial lining of the cervix. Although cervical cancer was the leading cause of cancer death in USA in 1930s, both the incidence and mortality from cervical cancer have decreased by almost one half since the early 1970s, largely as a result of widespread screening with the Pap-test. New technology for performing cervical cytology is evolving rapidly, as are recommendations for classifying and interpreting the results. In USA cervical cancer is the third most common gynecologic malignancy and in countries where cytologic screening is not widely available, cervical cancer remains common.
Cervical cytology screening programs have markedly reduced the cervical cancer incidence in the communities. The purpose of this document is to provide a review of the best available evidence on screening of cervical cancer.
Value of Cervical Cytology
Cervical cytology screening is, in many respects, the ideal screening test. Cervical cancer has a defined premalignant phase of many years, which allows repeated tests to significantly reduce the impact of individual false-negative test results. Cervical cytology is inexpensive and is readily accepted by women. Treatment is effective in reducing the chance of progression to invasive disease. Despite effective screening measures and treatment, it is estimated that 50% of the women who are diagnosed with cervical cancer have never had cervical cytology screening. Another 10% had not been screened within the 5 years before diagnosis. Thus, one approach to reducing the incidence and mortality of cervical cancer would be to increase screening rates among women who currently are not screened or undergo screening infrequently (1).
In some cases cervical cancer is undetected despite a recent screening test because of errors in sampling, interpretation, or follow-up. Sampling errors occur when dysplastic cells on the cervix are not transferred to the slide; errors of interpretation are attributed to lack of recognition of abnormal cells in laboratory. These two sources of false-negative test results are associated with 30% of the new cases of cervical cancer each year (2). The problem of errors in interpretation is compounded by inconsistency among cytologists.
Techniques on Cervical Cytology
Sampling involves collecting exfoliated cells from the ectocervix and endocervical canal and transferring them to a glass microscope slide or into a liquid transport medium for review. Patient preparation and proper provider technique can help optimize the collection of cells (3):
- Cells should be collected before the bimanual examination.
- Care should be taken to avoid contaminating the sample with lubricant.
- If testing for sexually transmitted diseases is indicated, cell collection for cervical cytology should be undertaken first.
- Ideally, the entire portio of the cervix should be visible when the sample is obtained.
- Routine swabbing of the discharge from the cervix may result in cytologic samples of scant cellularity.
- In an effort to reduce air-drying artifact, the specimen should be transferred and fixed as quickly as possible.
When performing cervical cytology by standard preparation, a single slide, combining both the endocervical and ectocervical samples, or two separate slides can be used. The most important consideration is rapid fixation. If liquid-based preparations are used, rapid immersion in liquid media is equally important.
In 1980s new devices were developed for enhancing the collection of exfoliated cells from the cervix. These included nylon brushes for sampling the endocervix and "broom" sampling devices, which simultaneously sample both the ectocervix and endocervix. These devices have been shown to increase the amount of cells captured from the transformation zone and to increase the amount of dysplastic cells collected when compared with cotton-tipped applicators and wooden Ayre's spatulas. In 1996 the US Food and Drug Administration approved the first of two currently available liquid-based thin-layer cytology preparations for cervical screening. In addition, automated, computer-based technologies have been marketed that use digitally scanned images to facilitate primary screening.
The nomenclature for reporting cervical cytology results has undergone several changes. The Bethesda System of reporting is the most widely used system in the United States (4). In 2001 the revised terminology which is widely used in USA is as follows:
- Specimen adequacy - slides are to be reported as "satisfactory" or "unsatisfactory" for interpretation. The presence or absence of an endocervical or transformation zone component is described in the narrative portion of the laboratory report, as are other quality indicators, such as partly obscuring inflammation or blood. If a slide is categorized as unsatisfactory, the reason should be specified. If abnormalities are found on an otherwise unsatisfactory slide, it will by definition be considered satisfactory for interpretation.
- Negative for intraepithelial lesion or malignancy - this designation should be used for slides with no cytologic evidence of neoplasia. This category includes findings previously designated as "benign cellular changes". When specific organisms are identified (eg, Trichomonas vaginalis, Candida species, Actinomyces species and cellular changes consistent with herpes simplex virus), they are reported and categorized as "negative for intraepithelial lesion or malignancy". Endometrial cells found in a woman aged 40 years or older will be listed under this category, but the finding of endometrial cells will not be reported routinely if noted in women younger than 40 years.
- Atypical squamous cells - the epithelial abnormality ASCUS has been replaced by "atypical squamous cells" (ASC) with subcategories "atypical squamous cells of undetermined significance" (ASC-US) and "atypical squamous cells cannot exclude HSIL" (ASC-H). The modifier of "favor reactive" was eliminated. The category ASC-H was introduced to include those cytologic changes suggestive of HSIL but lacking sufficient criteria for definitive interpretation.
- Atypical glandular cells - this term designates cells exhibiting atypia that are of glandular rather than squamous origin and replaces the term "atypical glandular cells of undetermined significance". The finding of atypical glandular cells on cytology is more likely to be associated with both squamous and glandular abnormalities than is ASC-US, and the work up required of atypical cells is more aggressive. The 2001 terminology subdivides atypical glandular cells by cell type, i.e., atypical endocervical cells, atypical endometrial cells, or atypical glandular cells not otherwise specified.
- Low-grade squamous intraepithelial lesions (LSIL) - the 2001 nomenclature combines cytologic findings of CIN 1 (mild dysplasia) and those consistent with human papillomavirus (HPV) infections into the category LSIL.
- High-grade squamous intraepithelial lesions (HSIL) - the 2001 nomenclature maintains the category of HSIL, which combines CIN 2 and CIN 3 (moderate dysplasia, severe dysplasia, and carcinoma in situ). Although the natural history of CIN 2 lies between CIN 1 and CIN 3, the virology if CIN 2 is more like CIN 3 than CIN 1 in its likelihood of representing aneuploidy and monoclonal proliferation with a single high-risk HPV type.
- The absence of endocervical cells or a transformation zone component on the cervical cytology sample may reflect that the transformation zone was not well sampled. This finding is common in pregnant women and in postmenopausal women in whom the transformation zone has receded into the canal. Pregnant women lacking endocervical cells or transformation zone component should have repeat cervical cytology screening postpartum.
Bethesda III System: Atypical Squamous Cells (ASC)
Source: Solomon D et al (5)
- Atypical Squamous Cells of Undetermined Significance (ASC-US)
- Changes symptomatic of SIL but lack criteria for definitive interpretation
- Represents 90% to 95% of ASC cases
- Half are positive for HPV
- 1% to 5% involve CIN grade 3
- Atypical Squamous Cells - Cannot exclude HSIL (ASC-H)
- Changes suggestive of HSIL but lack criteria for definitive interpretation
- Represents 5% to 10% of ASC cases
- 70% to 80% are HPV positive
- 20% to 25% involve CIN 3
- High positive predictive value for an underlying lesion characterized as CIN 2 or greater
- Reflects a mixture of CIN 2 and 3
- Poor reproducibility and interobserver agreement
Natural History of Cervical Neoplasia and Dysplasia
Infection with HPV is a necessary factor in the development of cervical neoplasia and dysplasia; however, most HPV-infected women will not develop significant cervical abnormalities. The infection is easily transmitted during sexual intercourse. Cigarette smoking and compromised immune system appears to play a role in some women. The once widely held concept that low-grade lesions may progress to invasive cancer is doubtful. It is observed many women present with CIN 2 and CIN 3 without prior CIN 1 lesions. Foci of CIN 1 and CIN 3 with different HPV types have been reported in some cervical lesions. A few cases of invasive cancer of the cervix have been reported despite continuous and appropriate screening.
A review of 30 years of the literature calculated pooled rates of progression from LSIL and HSIL to invasive caner to be 0.15% and 1.44%, respectively, over 24 months (6). In that analysis, 47% of LSIL and 35% of HSIL regressed to normal during the 2 year observation period. Cervical neoplasia and dysplasia develops in susceptible individuals in response to a sexually transmitted infection with a high-risk type of HPV. The cervix is especially vulnerable to this infection during adolescence when squamous metaplasia is most active. Human papillomavirus infections are commonly acquired by young women, but in most they are cleared by the immune system within 1-2 years without producing neoplastic changes. The risk of neoplastic transformation increases in those women whose infections persist. Most cervical squamous intraepithelial lesions do not progress to cervical cancer. It seems reasonable to begin cervical cancer screening approximately 3 years after initiation of sexual intercourse, but no later than age 21 years. Recognizing the time course in the progression of CIN and the unpredictable nature of follow-up in younger women, cytologic screening may be initiated earlier at the discretion of the healthcare providers.
Optimal Frequency of Cervical Cytology Screening
The optimal number of negative cervical cytology test results needed to reduce the false-negative rate to a minimum has not been demonstrated. Several practical considerations must be examined before biennial or triennial screening can be adopted as a national standard.
American Cancer Society (ACS) and American College of Obstetricians and Gynecologists (ACOG) recommendations for Cervical Screening:
- Approximately 3 years after the onset of vaginal intercourse.
- No later than 21 years of age.
- Women aged 70 years or older with an intact cervix who have had 3 or more documented, consecutive, technically satisfactory/normal/negative cervical cytology tests and no abnormal/positive cytology tests after the age of 60.
- Screening is recommended for women not previously screened, women for whom information about previous screening is unavailable, and women for whom past screening is unlikely.
- Vaginal cytology screening tests are not indicated after total hysterectomy for benign gynecologic disease.
Frequency of Screening:
- After initiation of cervical screening, perform annually with conventional cervical cytology smears or every 2 years using liquid-based cytology.
- Women 30 years of age or older who have had 3 consecutive, technically satisfactory normal/negative cytology results may be screened every 2 to 3 years unless they have a history of in-utero diethystillbestrol exposure, human immunodeficiency virus, or are immunocompromised.
- Women should be educated that a pelvic exam is not the same as a cytology or Pap test.
- Pelvic and rectal exams are important for the identification of other types of cancer and other gynecologic conditions.
- The goals of adolescent screening and referral are the detection and treatment of HSILs.
- False-positive cytology results and/or mild abnormalities on cervical cytology should not result in denial of health insurance coverage for women of any age.
- Healthcare providers should confirm insurance coverage of new cervical screening technologies prior to ordering tests.
Source: Saslow D et al (7)
HPV's Role In Cervical Dysplasia and Cancer
Human papillomavirus (HPV) is a sexually transmitted disease. The relationship between HPV infection and cervical cancer is known for decades. Over 100 types of HPV are known, and 13 to 15 of these are linked to cervical cancer. The subtype 16 (HPV-16) carries the highest risk for cervical cancer. Low-risk types that affect the genital tract usually manifest as genital warts. HPV is found in 99.7% of invasive cervical cancers and cancer/cervical intraepithelial neoplasia contains 1 of 13 oncogenic types. Millions of women in the United States and worldwide harbor HPV, but only a fraction develops cervical intraepithelial neoplasia or cancer. The prevalence of high-risk HPV infection is highest in women 20 to 24 years of age (24%) and decreases with age. When women older than 30 years of age have high-risk HPV infection, there is an increased risk for the development of high-grade lesions and cancer; women with persistent high-risk HPV infections are the population at greatest risk for developing cancer. Approximately 90% of HPV infections resolve within 2 years. Clinical progression to CIN 3 is mostly seen with high-risk HPV.
DNA Testing and Clinical Utility in Triage: Several methods exist for DNA testing of HPV. Hybrid capture (Hybrid Capture 2, Digene Corp, Gaithersburg, MD) is the most common method in clinical use. It allows the separation of low- and high-risk subtypes. DNA testing was found to have greater sensitivity in detecting CIN 3 or more advanced lesions and showed specificity comparable to a single additional cytologic test indicating ASC-US or greater. DNA testing for HPV is an important tool in the management of women with an ASC-US cytologic diagnosis. Other issues that may impact the clinical utility of HPV testing include (8):
- HPV-16 in normal cytology is the highest predictor of subsequent development of CIN.
- In women 29 years of age or older, HPV testing is 94% sensitive for CIN 3 and more advanced lesions, with a 31% rate of colposcopy referral. This equates to a 30% reduction in the rate of referral compared with HPV testing in younger women.
- Only 15% of women infected with an oncogenic HPV type with negative cytology will develop an abnormal Pap within 5 years; however, this risk increases with greater viral load.
- Women with negative cytology and negative HPV test results have a very low risk (0.16%) of developing CIN 3 over the next 45 months.
In any sizable population, even among women with evidence of cytologic abnormalities, there will be a few cases of cervical pre-cancer that will test high-risk HPV negative for one or more reasons (10).
HPV Vaccine Trials
Vaccines for HPV can be separated into 2 different types: those aimed at prevention and those that focus on treatment. For prevention trials, the vaccine must be given before any viral exposure, and vaccination is performed with viral-like particles that allow the body to build immunity. To date, the only vaccines available protect against specific types of HPV rather than HPV infection in general (9).
Preventive Vaccines: Multivalent vaccines that protect against different subtypes of high-risk HPV are being developed. The possibility of eradicating high-risk HPV subtypes such as 16, 18, 31, and 45 (80% of cancers) is very useful. However, the possibility of impacting the total number of cervical cancer cases in both developed and developing countries is projected to take many decades.
Therapeutic Vaccines: Evaluation of therapeutic vaccines is in the early stages. The following 3 Gynecologic Oncology Group (GOG) studies are in various stages of development:
- GOG9806: Vaccine therapy and detection of immunologic responses with HPV-16 E6/E7 peptides in patients with metastatic or locally advanced cervical cancer and other cancers carrying HPV.
- GOG9601: Phase I study of HPV E7 lipopeptide vaccine for the treatment of recurrent or persistent cervical cancer.
- GOG0197: Phase II study evaluating SGN-00101 (HSP-E7) fusion protein in women with CIN 3.
The relationship between HPV infection with high-risk subtypes and cervical cancer is well-established. Results of clinical studies have demonstrated that reflex HPV testing has a role in triaging ASC-US patients identified with liquid-based cytology in clinical practice but has no role in LSIL or more advanced cases. The clinical utility of combining HPV/cytology testing as an alternative to Pap testing alone in women 30 years of age and older may serve to increase the necessary interval between Pap tests. Several HPV vaccination trials are under way and promise to provide more insight into the exciting possibility of eradicating HPV infections and thus cervical cancer.
Healthcare providers should consider individualization in determining the time to begin screening, the interval between cervical cytology examinations, the age at which cervical cytology testing is no longer needed, and the testing methodology to be used. In addition to considering risk factors for cervical cancer, the provider ideally should be able to determine the patient's past screening history and reliability monitor the patient in the future. Yearly testing using cytology alone remains an acceptable screening plan. Regardless of the frequency of cervical cytology screening, women should be counseled that annual examinations, including pelvic examination, are still recommended.
- American Cancer Society. Cancer facts and figures 2007. Atlanta (GA): American Cancer Society; 2007:4
- Munoz N, Bosch FX, de Sanjose S, et al. Epidemiologic classification of human papillomavirus types associated with cervical cancer. N Engl J Med 2003;348:518-527
- ACOG Practice Bulletin: Clinical management guidelines for obstetricians-gynecologists. Number 45, Aug. 2003
- World Health Organization (WHO) Initiative for Vaccine Research. Human Papilloma Infection and Cervical Cancer. Geneva, Switzerland: WHO; 2008. http://www.who.int/vaccine_research/diseases/hpv/en/ . Accessed July 10, 2008
- Solomon D, Davey D, Kurman R, et al. The 2001 Bethesda System: terminology for reporting results of cervical cytology. JAMA 2002;287:2114-2119
- Ault KA, for the Future II Study Group. Effect of prophylactic human papillomavirus L1 virus-like particle vaccine on the risk of cervical intraepithelial neoplasia grade 2, grade 3, and adenocarcinoma in situ: a combined analysis of four randomized clinical trials. Lancet 2007;369:1861-1868
- Saslow D, Runowicz CD, Solomon D. et al. American Cancer Society guideline for the early detection of cervical neoplasia and cancer. CA Cancer J Clin 2002;52:342-362
- Lonky NM, Felix JC, Naidu YM, Wolde-Isachik G, Triage of atypical squamous cells of undermined significance with hybrid capture II: Colposcopy and histologic HPV correlation. Obstet Gynecol 2003; 101:481-489
- Kontsky LA, Ault KA, Wheeler CM, et al. A controlled trial of a human papillomavirus type 16 vaccine. N Engl J Med 2002;347:1645-1651.
- Castle PE, Cox TJ, Jeronimo J et al. An analysis of high-risk human papillomavirus DNA-negative cervical pre-cancers in the ASCUS-LSIL Triage Study (ALTS). Obstet Gynecol 2008;111:847-856
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