2023-08-03 05:01:31
A simple PCR test will replace the less reliable smear for women in the future: what do you need to know?
About 300,000 Flemish women between 25 and 64 are invited every three years for a free cytological examination, the so-called ‘smear’, in the fight against cervical cancer.
The World Health Organization (WHO) and other experts argue however, has long been in favor of replacing that test for women over the age of 30 with a test for the human papilloma virus (HPV). That virus is the main cause of cervical cancer, the fourth most important cancer for young women aged 25 to 44 in our country.
The HPV test immediately detects the human papilloma virus, usually through a PCR test, while the classic Pap smear looks for precancerous cells, which can eventually develop into invasive cancer cells. With an HPV test, therefore, intervention can be made much earlier.
Recently, the various governments in our country took the decision to generally introduce the HPV test instead of the cytological examination. That could possibly happen from the end of 2024.
‘Stephanie Van Houtven, the young politician who died of cervical cancer, has made an enormous contribution to speeding up the decision-making process in Belgium,’ says Marc Arbyn, cancer epidemiologist at Sciensano. ‘Already in 2015, the Federal Knowledge Center for Healthcare issued a positive recommendation for the HPV test. Although a lot of decisions still have to be made about the conditions of the screening, which HPV tests and which laboratories we use, who pays what and what to do if the result is positive.’
In 2021, more than 63 percent of the Flemish women who were invited had themselves screened for cervical cancer with a smear. With today’s knowledge, this would be better done with the HPV test. In the case of Stephanie Van Houtven, several smears turned out to be negative, even though the cancer was present in her body.
Why is the HPV test better than a Pap smear?
Marc Arbyn: The HPV test scores better in many areas. There is less chance of false negative results because the test is more sensitive than cytology. In addition, HPV research involves a machine test that looks for the DNA of the virus, just like we did during the covid period. A classical cytological test relies on the attention of the cytologist who must distinguish abnormal specimens under the microscope among a mass of cells. That is not always easy and foolproof. And because we detect the virus ourselves, which only leads to a possible cancer years later, we can extend the interval from three to five years. In the Netherlands, the interval for women older than 45 who tested negative for HPV before is even ten years. Finally, the HPV test is cheaper than the classic Pap smear.
Cytologists nevertheless believe that the HPV test is qualitatively unnecessary because the cytological examination has become much more efficient in recent years. Justifiably?
On: Indeed, for decades, cytologists have invested heavily in the research of cervical swabs. They know the subject very well. But the conclusions of the Knowledge Center report from 2015 are still not outdated. On the contrary. Since then, the evidence has only increased, even with the more advanced techniques of liquid cytology.
Will women not be needlessly alarmed and treated after a positive HPV test? A significant percentage of women will have to deal with the virus during their lifetime, which is usually cleared by the body itself.
On: Typically, HPV positivity is more common than cytologic positivity. So more women will indeed get bad news. To avoid overdiagnosis, it is important that we first and foremost offer the test to women aged 30 and older. After all, HPV infections are more common in young women and generally disappear spontaneously. The chance that HPV remains persistently present is greater from the age of 30. Second, in HPV-positive women, additional tests, such as a cytological examination and determination of the HPV type, will help to avoid unnecessary treatment. One treatment is to cut out a piece of tissue, but we know that this increases the risk of complications in pregnancy, such as preterm delivery.
What changes in practice for the patient?
On: As today, women will still be invited to the gynecologist or general practitioner for a free smear test in which cells are scraped from the surface of the cervix. The most important change occurs in the lab where a PCR test is performed on the sample instead of a microscopic examination for abnormal cells. Women between the ages of 25 and 30 would still receive the classic cytological examination. An abnormal result is followed by an HPV test.
In the Netherlands, people don’t even have to go to the doctor anymore, but women can take their HPV test themselves. An option for our country?
On: The HPV test can indeed be performed on a self-collected sample. This is the case in the Netherlands, Sweden, and Australia, where the test is used as a first-line approach for all women in addition to screening by a doctor. Because we still know too little about the long-term protection of a negative HPV test through self-sampling, I advocate a slightly more cautious approach and to offer the self-test in the future first to women who are usually not inclined to go to the GP or gynecologist so that we can also reach that risk group. Of course, there is a chance that the envelope with the self-test ends up unopened in the bottom drawer of the cupboard. That is why we are also investigating the possibility of having GPs offer self-sampling kits to their patients. That could possibly lead to a higher response.
Should women who have been vaccinated still get screened?
On: Yes, the vaccine does not protect against all HPV types. There are a dozen high-risk types. The vaccines contain most of the carcinogenic types, but not all of them. In addition, the age of the vaccination plays an important role. At the age of 15 years or younger, there is tremendous protection against all types contained in the vaccine, and there is also cross-protection on HPV types that are similar to the vaccine types. In older adolescents and very young adults, the protection is already somewhat less because the chance that one has already been in contact with the virus is greater. In older adults, protection is rather low. Thanks to the vaccine, boys are also protected against HPV, which may cause penile cancer, anus cancer, and cancer of the mouth and throat. Vaccination of both sexes also contributes to herd immunity.
Can we eventually eradicate cervical cancer in the future, thanks to vaccination and better screening?
On: The WHO has called on all governments in the world to eliminate cervical cancer as a ‘threat to public health’. That is, down to the level of rare disease or less than four cases per hundred thousand per year. Complete eradication of the disease will be difficult because the risk of false negative results is not absent with the HPV test either. There are different types of tests and some are more sensitive than others. There is also a rare chance that an HPV type that is not one of the twelve high-risk types will still develop into cancer. It is also possible that the DNA of the virus merges with human DNA, so that the piece of viral DNA that ensures a positive test disappears, but the piece of DNA that causes cancer is still present. That is why we propose to introduce a quality control system for the HPV test so that we can use the best possible HPV tests.]
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