Based on a pilot study carried out by the
provincial Public Health Laboratory (PHL) on the application of
human papillomavirus (HPV) DNA testing in cervical cancer screening,
a large-scale randomized controlled trial is under way in the
province. This study will enroll 12,000 women in the age group 30 to
69 years in the St. John's area and Montreal, and is expected to
provide an unbiased comparison between HPV DNA testing and Pap
cytology as cervical cancer screening tools, and will also determine
the costs of delivery of the two screening strategies. This study is
supported by a research grant from the Canadian Institutes of Health
Research. It is the only study of its kind in North America and
expected to be completed in 2006.
In the meantime, the PHL provides the
following information on cervical cancer and HPV, and the
application of the HPV DNA test in cervical cancer screening and ASC-US
triage.
Persistent infection with oncogenic HPV is
the primary cause of cervical cancer and its precursor lesions.
Therefore, testing for HPV can detect cervical cancer risk at an
early stage. However, the usefulness of the HPV DNA test is
dependent on the age of women being screened. In women under 25
years of age, HPV infection is common, but mostly transient and not
associated with cervical cancer risk. Therefore, HPV screening is
not recommended for women under 25 years. In contrast, in women over
30 years, a positive HPV DNA test is mostly indicative of persistent
infection, and no more than five per cent tend to have a positive
test. Also, about 95 per cent of cervical cancers occur in this age
group. Therefore, finding HPV infection in this age group is
considered significant regardless of Pap smear, as this is known to
be associated with an increased risk of cervical cancer. While the
HPV DNA test can serve as a useful screening tool for women over 30
years, this test is not currently offered for screening purpose
outside the above mentioned research study.
The application of the HPV DNA test as an
adjunct test in ASC-US triage has been well established. ASC-US Paps
account for nearly two-thirds of all Pap abnormality reported in the
province, but in the majority this is not a predictor of cervical
cancer risk. However, five to 17 per cent in this group could have
underlying HSIL and hence the indication for further follow-up. In
this context, the HPV DNA test can identify women who are at risk
for cervical cancer and allow for close surveillance of those
testing HPV positive. While the PHL has been providing the HPV DNA
testing service to OB/GYNs for a while, there is consideration to
offer this service for ASC-US triage at the family physician level.
For additional information, please
contact Dr. Sam Ratnam at the Public Health Laboratory at
709-777-6568.
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