Gynecologic Cytopathology: Past, Present and Future
Moderator: Annabelle Farnsworth
Section 4 -
Cervical Cancer Screening in the HPV Era
Mark H. Stoler
University of Virginia Health System
Click here to download handout in pdf format for the current section (142 KB)
The conventional Papanicolaou (Pap) smear is the world's most successful cancer screening test.
Improving knowledge of the interaction between human papillomaviruses (HPV) and the development of
cervical neoplasia continues to impact cervical cancer screening practice. Yet, the concept of combining
molecular testing with morphology for cervical screening is so revolutionary that the medical community
continues to debate choices regarding cervical cancer screening and practice. In the United States, the
adoption of HPV as an adjunctive primary screening test has been slow. The reasons for this lag in
implementation are complex. They undoubtedly reflect the interplay among long-established clinical
practice patterns, lack of education regarding the data supporting the recommendations for joint testing,
and a lack of understanding of the potential medicolegal impact of not performing what may well be a
superior mode of testing.
Diagnostic Reproducibilty: HPV for Quality Control
Clearly diagnostic reproducibility is critical to the practice of pathology as well as to the clinical
management of pathologically diagnosed cervical cancer and its precursors. Previous studies on the
reproducibility of cervical neoplasia diagnosis are best characterized as limited in size and for the
most part, statistically inadequate. The National Cancer Institute (NCI)-sponsored Atypical Squamous
Cells of Undetermined Significance-Low-Grade Squamous Intraepithelial Lesion (ASCUS-LSIL) Triage Study
(ALTS) was designed in part to compare reproducibility of both cytological and histological diagnoses.
During enrollment in the ALTS trial the pathologists interpreted 4,948 ThinPreps and 2,237 colposcopic
biopsies. The comparisons between the clinical center and QC groups were performed in a completely
masked manner. The conclusion of these analyses was that, regardless of specimen type, there was only
moderate interobserver reproducibility between the pathologist at the clinical center and the QC
pathology group. There was significant asymmetry in each class of comparison suggesting that there was a
systematic pattern of disagreement between the clinical center and QC pathologists, with QC pathologists
tending to give less severe interpretations in all three types of specimens.
Given this relatively low degree of reproducibility that exists even between expert pathologists,
clinicians need to be aware of this source of variability as well as the compounding variability due to
variations in colposcopic assessment and biopsy placement. Because of this, objective independent
methods of assessing diagnostic accuracy such as HPV testing should assume a more prominent role in the
management of patients with mild squamous abnormality on Papanicolaou smear.
HPV Testing as an Adjunct for Triage: Already a Standard
ALTS firmly established adjunctive testing for high-risk HPV as the standard of care for the triage of
patients with mildly abnormal cervical cytology. As noted above, high-risk HPV testing is directly
correlated with the degree of cytologic interpretive certainty. What this means is that high-risk HPV
testing can be used to control the quality of cytologic interpretations for an individual, group or
laboratory. More importantly, the ALTS trial clearly demonstrated that HPV testing is the most effective
method for the triage of patients who have an equivocal cytologic interpretation. The burden of ASCUS
diagnosis on clinical practice is substantial. The critical practice question for physicians treating
these patients is how to find the fraction of these patients who have significant high-grade precursor
lesions. Complementary studies have clearly shown that the majority of high-grade lesions found in
clinical practice actually come from the ASCUS group. Indeed, 60% of colposcopically derived biopsies
read as high-grade cervical intraepithelial neoplasia (CIN) come from patients who have Pap smears read
as either ASCUS or LSIL, yet ASCUS is an inherently irreproducible cytologic diagnosis. ASCUS is perhaps
better viewed as a statistical risk group in which the clinical challenge is to find the high-grade CIN
when the majority of these patients really harbor no evidence of clinical or colposcopic high-grade CIN.
In a series of papers that have come to be known as the ALTS "quartet," the essential finding of the ALTS
trial was that HPV triage was 92% sensitive for prevalent CIN3 in the ASC-US group while referring only
53% of patients for colposcopy. There was no combination of cytologic follow-up at any interpretive
threshold that equaled this level of sensitivity while referring the same or fewer patients to
colposcopy. Hence, HPV testing seemed to be the optimal triage method for detecting the critical
high-grade disease in this clinically large population of patients. Of additional interest to the
practicing clinician was the fact that HPV testing also improved the sensitivity of colposcopy.
Specifically, knowledge of HPV status significantly improved the colposcopic sensitivity of biopsy.
Before the ALTS trial, colposcopy was widely thought to be the gold standard for the detection of CIN.
ALTS clearly demonstrated colposcopy to be less sensitive than was previously perceived. Finally, while
HPV testing is an excellent triage method for equivocal cytology, in patients with cytologically
diagnosed LSIL, high-risk HPV testing has little utility. This is because at least 84% of patients with
LSIL on cytology are already high-risk HPV positive. Hence, HPV testing will not effectively triage
these patients in whom it was established that there is a 25% to 30% likelihood of detecting a high-grade
cancer precursor over 2 years.
Given the success of HPV testing for triage of patients with abnormal cytologic findings, the question
naturally arises as to whether HPV testing should become the standard of care for primary screening.
This is particularly relevant in patients older than the age of 30 in whom the prevalence of HPV is
falling while the relative prevalence of significant histologic abnormality is increasing.
HPV Testing for Primary Screening: The Time Has Come!
If one looks at the causes for cervical cancer screening failure in the United States, it is clear that
more than 50% of the patients in whom cervical cancer develops have never been screened, and another 10%
to 20% of those patients have not been screened in at least 5 years. However, at least 30% of the
patients in whom cervical cancer develops have had a "false negative" Pap smear and approximately half of
those false-negative results are due to sampling error while the remaining 50% actually are screening or
interpretive errors. While society recognizes the success of the "imperfect" Pap smear in reducing the
incidence of cervical cancer, the primacy of the Pap smear has been threatened because of the burden on
the pathology community inflicted by the problem of false-negative results. Any single cervical cancer
screening event may only be 50% sensitive for prevalent disease. Thus, it is only through the repetitive
application of independent screening events, at relatively short intervals, that the Pap smear "system"
is really efficacious. While it is possible for women who routinely have perfect annual screening
attendance to have very low rates of cervical cancer, even with perfect attendance, the system is
imperfect and false-negative results will continue to occur. So how do we minimize false-negative
results while at the same time maximizing the efficiency and decreasing the inconvenience of the cervical
cancer screening process? The practical possibilities include improving the quality of the sample,
improving the detection of abnormal cells in the sample, improving the accuracy of morphologic
interpretation, and taking morphology out of the equation. Thin-layer cytology has been widely
implemented and in many reports increases in sensitivity and specificity have been achieved although this
is controversial. One might further decrease the fatigue and consequent false-negative rate of screening
cytology samples by the implementation of automation systems. This, too, has had some marginal impact on
the rate of false-negative cytology. But both of these methods have not had the dramatic desired impact
on false-negative rates needed to decrease the frequency of adverse medicolegal events. Assuming most of
the optimization of cytology has already been completed, it is only logical to ask whether an independent
test for the etiology of the disease that does not require the subjectivity of the entire cytologic
process can improve the performance of primary screening.
The primary data supporting the utility of HPV testing in conjunction with cytology for screening consist
of several studies that evaluated more than 60,000 women in a variety of clinical settings. All studies
demonstrated that HPV testing was more sensitive than cervical cytology regardless of the clinical
setting. At such high levels of sensitivity, many have been concerned that too many patients would be
referred to colposcopy, and those referred would fail to have identifiable lesions. Surprisingly, HPV
testing achieved specificities that were comparable to or only slightly less than those with cytology
alone. This undoubtedly reflects the problem of interpretive variability inherent in morphologic
assessment. HPV testing has been shown to be more sensitive than cytology, is more reproducible than
cytology and, because of the high sensitivity of combined testing, the consequent high negative
predictive value in a low prevalence population provides for less frequent screening, which ultimately
may increase the compliance of patients with screening recommendations.
So why has HPV testing for primary screening made such a small impact on clinical practice? Clearly,
clinicians are concerned about the need for counseling patients, especially regarding the significance of
HPV positivity in the setting of a negative cytology. Perhaps a bigger concern is the change in practice
surrounding interval extension. However, these concerns have to be balanced by societal and
epidemiologic perspectives. The best strategy for preventing cervical cancer is to use the most accurate
test at the longest possible interval.
The standard of care is established in professional communities based on consensus. This consensus can
be brought about through the interaction of experts, medical literature and individual or local practice.
Unfortunately, best-practice standards often conflict with other interests. The best test may not be the
most affordable test. The system that leads to maximal liability protection may be in conflict with the
needs of both payers and patients in terms of cost effectiveness vs. patient protection. Is the
conventional dry-slide Pap smear still acceptable for cervical screening? Certainly, the "more-than-50%"
rule in terms of standard of care would seem to suggest that conventional Pap smears are not the
"standard of care" in many communities. Of course, the logical extension of such reasoning is to ask
whether and when a laboratory will stop processing conventional Pap smears as "acceptable" specimens. In
many academic settings where conventional Pap smears account for less than 5% of routine specimens, the
ability to adequately train practitioners on the interpretation of conventional preparations may become
Likewise, there seems to be a large gap between the published data regarding HPV testing efficacy and the
medical community's understanding of the complexities of the underlying biology and science. Is the need
for HPV testing a patient, clinician, or laboratory judgment? Who determines the adequacy of a testing
specimen? If a blood test is delivered in the wrong type of collection tube or in an inadequate volume,
does the laboratory not have the right to reject the specimen? Up until the time of publication of the
data supporting the FDA's approval of HPV testing as an adjunct for primary screening, it was clear that
there seemed to be several ways to screen for cervical cancer. All methods, that is, conventional Pap
smears, liquid-based cytology, and so on, were "accepted." However, some methods seem to have a
significant false-negative rate. Clearly, from a legal perspective, false-negative results may cause a
bad patient outcome. Bad patient outcomes ultimately result in bad financial outcomes for practitioners.
The practitioners that seem most at risk are pathologists, because pathologists are responsible for
accepting, processing, and rendering reports on specimens submitted to laboratories for cervical cancer
Hence, from a legal perspective, it would seem that a testing paradigm that maximizes sensitivity while
minimizing false-negative results would result in optimal patient care and minimize malpractice risk for
pathology laboratories. Liquid-based cytology combined with HPV testing might be suggested (from the
legal perspective) as the only modality acceptable for cervical cancer screening. In such a system,
false-negative results would be virtually eliminated. Hence, screened women might be almost guaranteed
to avoid invasive cervical cancer. Pathologists might get sued less frequently. The theoretical risk
exposure for not following practice guidelines would be transferred to laboratories who continue to
accept specimens that are less optimal or to gynecologists and other practitioners who fail to follow
contemporary screening guidelines.
The Possible Near Future: HPV First Then (or no) Cytology
In the short term, combining HPV testing with cytology screening costs more money. Any system that costs
more money has to overcome the inertia against increased expenditure that is inherent in our current
payment system. The ultimate question, therefore, is whose interest is controlling: the interest of
payers or the interest of patients, and, by extension, the physicians who treat those patients? If the
data supporting the introduction of HPV testing as an adjunct to cervical cancer screening are valid,
then it would seem that ultimately the best medicine for patients should ultimately lead to better and
more rational medical practice. Indeed, just-published data imply that using HPV testing to screen for
cervical cancer could have a dramatic impact not only in the United States, but also on a worldwide
Even more controversial but logical is the concept that HPV testing as the more sensitive test should be
the primary screening test. Cytology would be a potential triage tool for HPV rather than the other way
around. While potentially threatening to some such a move is not only a logical way to save money, but
recent data suggest that it can be essentially as effective as doing both tests on all patients.
Obviously human papillomaviruses are the etiologic agent for a significant spectrum of pathology. The
ideal solution to this plague upon society would be the elimination of these viruses through prophylactic
vaccination. The era of prophylactic vaccines is upon us. A large-scale phase III trial of a
quadrivalent VLP vaccine against HPVs 6/11/16 and 18 is ongoing, but the FDA data for the per protocol
analysis demonstrated 100% efficacy for all cervical and vulvar pathologies related to the vaccine types
Ultimately multivalent vaccines seem likely. The implications of societal HPV vaccination on screening
systems, lesional incidence, cost-benefit analyses, etc. are complex, stimulating and are sure to fuel
vigorous debate for years to come.
- Bosch FX, Lorincz A, Munoz N, Meijer CJ, Shah KV. The causal relation between human papillomavirus and cervical cancer. J Clin Pathol. 2002;55:244-265.
- Stoler MH, Schiffman M. Interobserver reproducibility of cervical cytologic and histologic interpretations: realistic estimates from the ASCUS-LSIL Triage Study. JAMA. 2001;285:1500-1505. Abstract
- Kinney WK, Manos MM, Hurley LB, Ransley JE. Where's the high-grade cervical neoplasia? The importance of minimally abnormal Papanicolaou diagnoses. Obstet Gynecol. 1998;91:973-976.
- Stoler MH. Testing for human papillomavirus: data driven implications for cervical neoplasia management. Clin Lab Med. 2003;23:569-583.
- ASCUS-LSIL Triage Study (ALTS) Group. Results of a randomized trial on the management of cytology interpretations of atypical squamous cells of undetermined significance. Am J Obstet Gynecol. 2003;188:1383-1392.
- ASCUS-LSIL Triage Study (ALTS) Group. A randomized trial on the management of low-grade squamous intraepithelial lesion cytology interpretations. Am J Obstet Gynecol. 2003;188:1393-1400
- Cox JT, Schiffman M, Solomon D. Prospective follow-up suggests similar risk of subsequent cervical intraepithelial neoplasia grade 2 or 3 among women with cervical intraepithelial neoplasia grade 1 or negative colposcopy and directed biopsy. Am J Obstet Gynecol. 2003;188:1406-1412.
- Guido R, Schiffman M, Solomon D, Burke L. Postcolposcopy management strategies for women referred with low-grade squamous intraepithelial lesions or human papillomavirus DNA-positive atypical squamous cells of undetermined significance: a two-year prospective study. Am J Obstet Gynecol. 2003;188:1401-1405.
- Nanda K, McCrory DC, Myers ER, et al. Accuracy of the Papanicolaou test in screening for and follow-up of cervical cytologic abnormalities: a systematic review. Ann Intern Med. 2000;132:810-819.
- Stoler MH. Advances in cervical screening technology. Mod Pathol. 2000;13:275-284.
- Kulasingam SL, Koutsky LA. Will new human papillomavirus diagnostics improve cervical cancer control efforts? Curr Infect Dis Rep. 2001;3:169-182.
- Kulasingam SL, Hughes JP, Kiviat NB, et al. Evaluation of human papillomavirus testing in primary screening for cervical abnormalities: comparison of sensitivity, specificity, and frequency of referral. JAMA. 2002;288:1749-1757.
- Lorincz AT, Richart RM. Human papillomavirus DNA testing as an adjunct to cytology in cervical screening programs. Arch Pathol Lab Med. 2003;127:959-968.
- Cuzick J, Clavel C, Petry KU, et al. Overview of the European and North American studies on HPV testing in primary cervical cancer screening. Int J Cancer. Sep 1 2006;119(5):1095-1101.
- Smith RA, Cokkinides V, Eyre HJ. American Cancer Society guidelines for the early detection of cancer, 2003. CA Cancer J Clin. 2003;53:27-43.
- American College of Obstetricians and Gynecologists. ACOG Practice Bulletin. Clinical Management Guidelines for Obstetrician-Gynecologists. Number 61, April 2005. Human papillomavirus. Obstet Gynecol. 2005;105:905-918.
- Wright TC Jr, Schiffman M, Solomon D, et al. Interim guidance for the use of human papillomavirus DNA testing as an adjunct to cervical cytology for screening. Obstet Gynecol.2004;103:304-309.
- Goldie SJ, Gaffikin L, Goldhaber-Fiebert JD, et al. Cost-effectiveness of cervical-cancer screening in five developing countries. N Engl J Med. 2005;353:2158-2168.
- Schiffman M, Castle PE. The promise of global cervical-cancer prevention. N Engl J Med. 2005;353:2101-2104.
- Ronco G, Segnan N, Giorgi-Rossi P, et al. Human papillomavirus testing and liquid-based cytology: results at recruitment from the new technologies for cervical cancer randomized controlled trial. J Natl Cancer Inst. Jun 7 2006;98(11):765-774.
- Goldie SJ, Kohli M, Grima D, et al. Projected clinical benefits and cost-effectiveness of a human papillomavirus 16/18 vaccine. J Natl Cancer Inst. Apr 21 2004;96(8):604-615.
- Harper DM, Franco EL, Wheeler C, et al. Efficacy of a bivalent L1 virus-like particle vaccine in prevention of infection with human papillomavirus types 16 and 18 in young women: a randomised controlled trial. Lancet. Nov 13-19 2004;364(9447):1757-1765.
- Villa LL, Costa RL, Petta CA, et al. Prophylactic quadrivalent human papillomavirus (types 6, 11, 16, and 18) L1 virus-like particle vaccine in young women: a randomised double-blind placebo-controlled multicentre phase II efficacy trial. Lancet Oncol. May 2005;6(5):271-278.