HPV DNA testing: Is primary screening now within reach?

HPV triage is being rolled out across England as part of the NHS Cervical Screening Programme; Dr Tracy Huggins investigates the benefits of HPV testing and its potential as a primary screening tool

Each year, approximately 3.35 million women are screened in England as part of the NHS Cervical Screening Programme¹. Since the introduction of the call/recall programme in 1988, it has been estimated that up to 3,900 cases of invasive cervical cancer and around 4,500 deaths are prevented each year in the UK^2,3. Sadly, despite the programme’s success, 2,938 women are diagnosed with invasive cervical cancer every year in the UK and cervical cancer is the most common cancer in females aged under 35⁴. Furthermore, there has been a 77% increase in the incidence of cervical cancer in the 25-29 age group over the last ten years⁵ and the Human Papilloma Virus (HPV) has been found in almost 100% of all cervical cancers⁶. HPV-16 and HPV-18 are the two most oncogenic sub-types of the virus and are thought to be responsible for approximately 70% of all cervical cancers⁷. Although HPV vaccination is now available, studies suggest that up to 80% of people in the UK are infected with the HPV virus at some time during their lifetime, highlighting a pressing need for HPV screening in order to identify those women at highest risk of developing cervical cancer⁴.

Cervical cytology, first with the Papanicolaou (Pap) smear and now with liquid-based cytology, has been the traditional method for cervical screening in the UK, and has contributed substantially to decreasing rates of invasive cervical cancer and associated mortality. However, recent scientific developments have opened the way to further enhancements of the screening programme by providing earlier detection of pre-cancerous and cancerous lesions.

Studies have shown that HPV DNA testing has a higher sensitivity for detecting cervical pre-cancer and cancer than cytology and provides greater reassurance for screen-negative women than can be offered by routine cytology⁸. The ATHENA (Addressing THE Need for Advanced HPV Diagnostics) study – the largest registration study ever conducted for a diagnostic product, involving more than 47,000 women in the USA – supports these findings⁹.

[caption id="attachment_27272" align="alignright" width="200" caption="Electron micrograph of a negatively stained human papilloma virus"][/caption]

The ATHENA study evaluated the cobas HPV test – a fully automated HPV DNA test that uses amplification of target DNA by the Polymerase Chain Reaction (PCR) and nucleic acid hybridisation to simultaneously detect HPV-16, HPV-18, and a pool of 12 other HPV high-risk genotypes (31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66 and 68) at clinically relevant levels¹⁰. The study found a total of 1,923 women (4.1%) to have atypical squamous cells of undetermined significance (ASC-US). The study demonstrated the ability of the cobas HPV test to individually detect HPV-16 and HPV-18, and it validated the test for triage of patients with an equivocal smear result⁹. Importantly, the study also demonstrated that more than one in ten women aged 30 years or older who tested positive for HPV genotypes 16 and/or 18 by the cobas HPV Test had cervical pre-cancer despite their smear test being normal⁹.

HPV triage is currently being rolled out as part of the NHS Cervical Screening Programme. Initially, HPV testing will automatically be undertaken on any routine cytology sample that is reported as borderline or showing mild dyskaryosis. Women who test negative for HPV will be returned to routine screening every 3-5 years depending on their age, while those who test positive will be referred for colposcopy. An HPV ‘Test of Cure’ is also being introduced for women who have undergone treatment for high-grade cervical intraepithelial neoplasia (CIN) to determine the presence of any residual disease.

The introduction of HPV triage and ‘Test of Cure’ comes after careful evaluation in feasibility pilot studies conducted at six sentinel sites in England (Bristol, Norwich, Liverpool, Manchester, Northwick Park and Sheffield)^{6, 11}. Although rates of referral for colposcopy increased as a result of using HPV triage, these studies suggest that HPV testing was both effective and cost-efficient, allowing approximately one-third of all borderline and mildly dyskaryotic women to be returned immediately to routine recall, thereby reducing the burden on cytology services¹¹ and saving the NHS an estimated £16 million per year⁵.

As part of the HPV testing implementation, rigorous Quality Assurance systems have been established. Laboratories wishing to undertake HPV testing are required to handle a minimum of 35,000 cytology samples per year; to have sufficient capacity to deal with the increased colposcopy workload; to offer women their cervical screening test result within 14 days; and to have an effective training programme for local professionals. Laboratories are also required to take part in External Quality Assurance (EQA) and participate in an accredited QA scheme such as the UK NEQAS scheme for HPV.

Current guidelines for cervical screening rely predominantly on cytology testing to determine the risk of cervical cancer, despite the fact that cytology alone misses around 23% of cervical pre-cancerous lesions in a single round¹². HPV DNA testing has a sensitivity of approximately 97% for cervical cancer and its precursor lesions, as documented in a meta-analysis of studies involving over 60,000 women¹². This suggests that testing for high-risk HPV genotypes would be a far more sensitive and efficient strategy for primary cervical screening than using cytology testing.

A recently-published sub-analysis of the ATHENA study demonstrated that HPV DNA testing using the cobas HPV test was significantly more sensitive than cytology alone in detecting women with CIN3 or worse⁸, confirming the findings of other studies conducted in Europe. The risk of CIN3 or worse after a negative HPV test was found to be far lower than after negative cytology, and the women positive for HPV but negative by cytology had a high risk of CIN3 or worse⁸. Women with HPV-16 and/or HPV-18 accounted for approximately 70% of the cervical cancers found; suggesting the detection of these two HPV sub-types may enable the rapid identification of those women at increased risk of CIN3 or worse who need immediate colposcopy.

At a time when England is introducing HPV testing for triage of cytology, latest studies support using a clinically-validated HPV test for primary screening, with cytology used only to triage women positive for HPV^{13, 14}. High risk HPV testing (and genotyping for HPV-16, HPV-18 or both) could offer cost-effective and safe primary cervical screening and has the potential to improve laboratory efficiencies. The Advisory Committee on Cervical Screening – which advises Health Ministers in England on the effectiveness and its efficiency of the cervical screening service, and pertinent developments to enhance the service – is actively looking to pilot HPV testing as a primary screen. A decision on a pilot is expected later this year (Hansard, House of Commons Written Answers 11 July 2011: Column 100W).

The evidence for HPV DNA testing is overwhelming and women should be reassured by its adoption in the cervical screening programme. Moving forward, its proven benefits in early detection promises to further improve the cervical screening service providing women and healthcare professionals greater confidence in an accurate result.

References

1. NHS Cervical Screening Programme. Cervical cancer – incidence, mortality and risk factors: http://www.cancerscreening.nhs.uk/cervical/cervical-cancer.html.
2. Sasieni PD, Cuzick J, Lynch-Farmery E. Estimating the efficacy of screening by auditing smear histories of women with and without cervical cancer. The National Co-ordinating Network for Cervical Screening Working Group. Br J Cancer. 1996;73:1001-5.
3. Peto J, Gilham C, Fletcher O, Matthews FE. The cervical cancer epidemic that screening has prevented in the UK. Lancet. 2004;364:249-56.

4. Cancer Research UK, Cervical cancer risks and causes, 6 May 2011. http://cancerhelp.cancerresearchuk.org/type/cervical-cancer/about/cervical-cancer-risks-and-causes
5. NHS Cervical Screening Programme. Improving efficiency. Annual Review 2011. Available at: http://www.cancerscreening.nhs.uk/cervical/publications/cervical-annual-review-2011.pdf.
6. NHS Cervical Screening Programme. Evaluation of HPV/LBC cervical screening pilot studies. Report to the Department of Health. Revised October 2004. Available at: http://www.cancerscreening.nhs.uk/cervical/evaluation-hpv-2006feb.pdf.
7. Howell-Jones R, Bailey A, Beddows S, et al. Multi-site study of HPV type-specific prevalence in women with cervical cancer, intraepithelial neoplasia and normal cytology, in England. Br J Cancer 2010;103:209-16.
8. Castle PE, Stoler MH, Wright TC Jr, et al. Performance of carcinogenic human papillomavirus (HPV) testing and HPV16 or HPV18 genotyping for cervical cancer screening of women aged 25 years and older: a subanalysis of the ATHENA study. Lancet Oncol. 2011;12:880-90.
9. Stoler MH, Wright TC Jr, Sharma A, et al. High-risk human papillomavirus testing in women with ASC-US cytology: results from the ATHENA HPV study. Am J Clin Pathol. 2011;135:468-75.
10. Castle PE, Sadorra M, Lau T, et al. Evaluation of a prototype real-time PCR assay for carcinogenic human papillomavirus (HPV) detection and simultaneous HPV genotype 16 (HPV16) and HPV18 genotyping. J Clin Microbiol. 2009;47:3344-7.
11. Kelly RS, Patnick J, Kitchener HC, et al. HPV testing as a triage for borderline or mild dyskaryosis on cervical cytology: results from the Sentinel Sites study. Br J Cancer. 2011;105:983-8.
12. Cuzick et al. “Overview of European and North American studies on HPV testing in primary cervical cancer screening.” International Journal of Cancer.
13. Rijkaart DC, Berkhof J, Rozendaal L, et al. Human papillomavirus testing for the detection of high-grade cervical intraepithelial neoplasia and cancer: final results of the POBASCAM randomised controlled trial. Lancet Oncol. 2012;13:78-88.
14. Kitchener HC. Gilham C, Sargent A, Bailey A, Albrow R, Roberts C, Desai M, Mather J, Turner A, Moss S, Peto J.  A comparison of HPV DNA testing and liquid based cytology over three rounds of primary cervical screening: Extended follow up in the ARTISTIC trial. Eur J Cancer 2011;47(6):864-87