Shifting from cytology to HPV testing for cervical cancer screening in Canada.

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Authors: Emily Delpero and Amanda Selk
Date: May 2, 2022
From: CMAJ: Canadian Medical Association Journal(Vol. 194, Issue 17)
Publisher: CMA Impact Inc.
Document Type: Article
Length: 2,067 words
Lexile Measure: 1850L

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Infection with high-risk strains of the human papillomavirus (HPV) is a known prerequisite for developing cervical cancer. (1) Soon, a test for high-risk strains of HPV will replace the Papanicolaou (Pap) test for routine cervical cancer screening in Canada. Unlike the Pap test, which requires a cytopathologist to detect precancerous cervical cells, testing of a cervical sample for HPV subtypes uses polymerase chain reaction (PCR). Australia, the Netherlands and the United Kingdom have adopted the HPV testing model for cervical screening, and it is also endorsed by the American Cancer Society. (2) A recent review by the Canadian Agency for Drugs and Technologies in Health considered available evidence; its report concluded that HPV PCR testing of cervical samples is better at detecting precancer or cancer than Pap testing and would decrease the overall cost of screening. (3) However, shifting to this new screening modality will mean overhauling existing algorithms for age and screening intervals, changing resource allocation and educating physicians and patients. We discuss why and how cervical screening will need to change in Canada with the adoption of the new test.

Current screening approaches acknowledge that Pap testing has a high specificity of 96.8% (4) but a low sensitivity (55.4%), which means that screening misses almost half of existing abnormalities. A short interval for repeat testing (every 2-3 years, starting between the ages of 21 and 25, depending on the province) mitigates harm, as subsequent testing is likely to detect previously missed pathology in populations with relatively high disease prevalence.

Cervical cancer rates have declined in Canada in the 50 years since the introduction of cervical screening programs. Between 1978 and 2006, cervical cancer incidence dropped from 20.05 to 12.66 per 100 000, (5) likely a result of population screening efforts (https://s22457.pcdn.co/wp-content/uploads/2019/01/Cervical -Cancer-Screen-Quality-Indicators-Report-2016-EN.pdf). In 2022, the projected age-standardized incidence rate for cervical cancer in Canada is 7.5 per 100 000. (6) Primary prevention with routine vaccination against high-risk HPV for school-age children is expected to further decrease disease incidence. Recent data from the UK modelled reduced risk for precancerous lesions in vaccinated cohorts, with near elimination of these lesions in those who were immunized at middle-school age. (7) A Swedish cohort study also linked HPV vaccination to reduced risk of cervical cancer at the population level. (8) Rates of precancerous and cancerous cervical disease in Canada are expected to decline in a similar fashion. This will lower the positive predictive value of the Pap test. (9) In the context of reducing disease prevalence and known limitations of Pap tests, a new strategy to maintain disease detection rates is needed.

Human papillomavirus DNA PCR testing has a higher sensitivity than cytology-based screening (94.6% v. 55.4%), but a lower specificity (94.1% v. 96.8%). This means that a greater proportion of patients without cervical disease are likely to receive a positive test result. (10) However, with increasing HPV vaccine uptake and decreasing prevalence of high-risk HPV infection, HPV testing is expected to confer fewer false positives than Pap testing, while maintaining a...

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Gale Document Number: GALE|A702029671