Molecular technologies target HPV testing in fight against cervical cancer
Adding to traditional screening for women, newer DNA and mRNA tests are highly sensitive in detecting the cancer-causing virus.
Pap test effective but can be enhanced with advancments in diagnostics
According to the Public Health Agency of Canada,1 in 150 women are expected to develop cervical cancer during her lifetime.
The good news is that the rates of this cancer have been falling for decades, which public health officials attribute to increased use of the Pap smear test. That has been the chief way of detecting pre-invasive lesions. Now, newer molecular technologies are showing even more promise for enhancing current screening, including mRNA and DNA tests for HPV, the virus that’s the main precursor for cervical cancer. In essence, HPV tests screen for the
presence of the virus. A Pap test looks for cellular changes caused by the virus, which can lead to cancer. Cancer experts say an effective screening strategy will combine both to maximize their benefits.
“Pap testing is very effective, and has reduced cervical cancer tremendously. But I would like to see the most sensitive and specific test used for screening – for me, that’s mRNA tests,” says Dr. Max Chernesky, Professor Emeritus in the Departments of Pediatrics, and Pathology and Molecular Medicine, St. Joseph’s Healthcare, McMaster University, Hamilton.
What are the benefits of including HPV testing for cervical cancer screening? Consider that reading the results of Pap smears can be subjective and result in a high number of false negatives, says Dr. Eduardo Franco, Chair, Department of Oncology, and Director, Division of Cancer Epidemiology, at McGill University in Montreal.
“We’ve known this for some time, and the way we compensate is by doing annual Pap tests,” says Dr. Franco. “Cervical cancer may take 20 years to develop, so we have a lot of opportunity to detect the cancer before it causes clinical trouble.”
During a Pap test, a small sample of cells is removed from the cervix to be examined under a microscope. The test is used to screen for and help diagnose pre-cancerous conditions and cervical cancer. Looking for the HPV virus in this sample can add additional sensitivity and disease detection.
More advanced screening is objective and consistent
Pap tests are well established, and will remain an essential part of screening. Yet these tests will likely work in concert with HPV screening.
HPV — the human papillomavirus — is one of the most common sexually-transmitted infections. The Public Health Agency of Canada estimates that more than 70 percent of sexually-active Canadian men and women will get an HPV infection in their lives.
Contracting HPV does not necessarily mean a woman will go on to develop cervical cancer. The vast majority of HPV infections go away with- out treatment. But some persistent HPV infections can be cancer-causing. HPV is responsible for more than 99 percent of all cervical cancers.
Molecular technologies include DNA and mRNA (messenger RNA, a large family of RNA molecules that convey genetic information). Instead of a technician, a machine reads the results after a series of chemical reactions — “It’s always consistent, and always the same quality of results,” Dr. Franco says.
With the newer molecular technologies, in a group of 100 women with a pre-cancerous lesion, a DNA or mRNA test will catch it 95 percent of the time — only 5 percent false negatives.
“Cervical cancer may take 20 years to develop, so we have a lot of opportunity to detect the cancer before it causes clinical trouble.”
— Dr. Eduardo Franco
In theory, says Dr. Franco, that means you can lengthen the screening interval, which will reduce health care costs.
HPV screening isn’t standard in provincial health coverage
In Canada, labs have access to several forms of DNA testing for HPV and one type of mRNA test (to date). Dr. Chernesky explains that if you find DNA in a sample, it signifies an HPV infection. But mRNA is a more focused test – “more closely aligned with the cancerous process,” says Dr. Chernesky.
The mRNA test is a nucleic acid amplified test – in other words, a molecular technique used to detect the genetic material of an infecting organism or virus. In this case, the mRNA test detects 14 high-risk strains of HPV that are associated with cervical cancer and pre-cancerous lesions.
Even among HPV high-risk infections, 90 percent clear within two years. It’s unlikely that an HPV test would be used as a sole diagnostic tool. Suspicious cases would require further testing.
Canadians can get these advanced molecular tests in private labs, but they’re not currently on the fee schedule for most provincial health coverage. Yet Dr. Chernesky, who has conducted major research in the development of laboratory diagnostic techniques, feels it’s just a matter of time before the newer DNA and mRNA tests are part of routine primary screening.
“When we do go to a screening program like that, the impact should be that we will diagnose abnormalities more quickly, and be able to intervene quicker to reduce the number of cancers,” says Dr. Chernesky.