Screening and vaccinating against cervical cancer

Recent media attention has highlighted the awful plight of women affected by cervical cancer. In this article I’ll try and answer some basic questions about this cancer and, more importantly, what we can all do to reduce the chances of developing this condition. Robert O’Connor, Head of Research at the Irish Cancer Society, writes.

What is cervical cancer and how does it happen?

The cervix is a tube of tissue connecting the vagina to the uterus and it plays a vital role in pregnancy and birth. Unfortunately, it is also a site for cancer growth. Cervical cancers are caused by specific strains of a virus called HPV.

HPV viruses live on the lining cells of the cervix, anus and throat of women and men and are incredibly infectious, with any form of intimate or sexual contact allowing the virus to pass from one person to another. Up to one in four young adults may be carrying infection at any given time. Infection will not usually show any signs or symptoms at all and there is no direct treatment. As a result, most people will be infected over their lifetime and condoms do not assure protection.

Close to 9/10 women will clear an infection within 18 to 24 months after exposure. However, if the HPV virus is not cleared it can start to cause changes and abnormalities in the cells as it grows, over time these changes can become more severe and the cells become cancerous, invading surrounding tissues.

There are two main types of cervical cancer, roughly 7/10 cases arise on the outside lining cells but approximately 2/10 arise deeper in the glands of the cervix. These glandular cancers, called adenocarcinomas, are much more difficult to detect and tend to be more aggressive. The evolution of an infected cervical cell to an overt cancer is gradual and usually takes 15-20 years. In Ireland, in their lifetime, roughly 1/10 women will need treatment for precancerous abnormalities, 1/120 will develop cervical cancer and 3/1,000 will die from this disease.

HPV can cause other cancers in women and in men, especially cancers of the head and neck. Each year in Ireland, 420 people develop a HPV-caused cancer with roughly three-quarters of them being female and one-quarter of them male.

What is screening and what does it try to do?

Cancer can only be diagnosed by a complex series of invasive and time-consuming investigations at which point it may already be life threatening. However, since we know that cervical cancer exists for many years in a ‘pre-cancerous’ state, finding and removing these abnormal cells before they become a cancer can reduce the chances of it developing.

Cervical cancer screening uses a small brush to sample some cells which are then examined by a specialist under a microscope to see if abnormalities are present. If abnormal cells are found, a special more invasive examination can be conducted to examine the cervix and, if necessary, remove abnormal tissue.

Some early abnormalities will regress and disappear themselves and hence the best treatment sometimes may be to watch more closely without any treatment, worrisome and all as that may be for a woman. International research has identified the optimal use of screening as a public health measure to increase the chances of catching abnormal cells before a cancer develops while reducing the number of samples taken and the inconvenience of the test for women.

Indeed, sampling too early (below the age of 25) or too often (for example, annually) has been shown to cause more harm without reducing the chances of cervical cancer death. This is why the Irish cervical cancer screening programme provides free tests for women from the age of 25 every 3 years (later becoming 5 years if multiple smears are negative).

What are the limitations of screening?

There are several inherent limitations in cervical screening:

1. The sampling brush only makes contact with the head of the cervix and hence cannot reliably detect deeper glandular changes or adenomacarcinomas.

2. The brush may fail to collect cells from smaller areas of abnormality.

3. Cancerous changes can occur between smears

4. It takes years of training to be able to see the subtle changes in a handful of cells against a background of thousands of other normal cells and even experienced experts can differ on their interpretation of such findings let alone the human errors that can occur where something is simply missed.

These issues will unfortunately only become evident after a cancer has developed. Hence, even a high-quality screening service, such as the one used in Ireland, can only detect and prevent between six and seven out of 10 cases. It is not a cancer test, but engagement with the programme greatly stacks the odds in favour of a woman not developing or dying from cervical cancer. However, it cannot guarantee this outcome.

In Ireland, the background rate of cervical cancer was rising prior to the introduction of screening in 2008. Since that date, up to 8/10 women have engaged with the programme with cervical cancer rates dropping annually by 7 per cent. Diagnosis rates have halved and are still falling. Annually over 250,000 smears are conducted and to date the programme has detected over 80,000 abnormalities with more that 50,000 of these being high grade requiring treatment.

Notwithstanding the successes of the programme, it will always fail to pick up some precancers, in small part this can result from unavoidable human error, but it is mostly due to the inherent limitations of the test itself. The consequences for such limitations can be very grave. Even with multiple ‘clear’ smears, any cervical symptoms should be urgently investigated. Cervical cancer is typically diagnosed in fertile women, many of whom will be young mothers.

“No screening technology will eliminate cervical cancer risk, however, screening goes hand-in-hand with vaccination to allow, for the first time, for the possibility of the effective elimination of this form of cancer within our lifetime.”

Treatment and its emotional and physiological consequences can be devastating and life changing for these women, their partners and their families. Two-fifths of patients will succumb to their disease within five years of diagnosis. This is why it is so important to seek to eliminate this form of cancer.

What is the future?

Modern technology now allows for the accurate detection of the presence of the HPV virus itself and hence a more sensitive indicator of possible early cancer risk. On the recommendation of an independent analysis by HIQA, the national cervical cancer screening programme is transitioning to using a HPV test as the primary screen technology.

Using a similar brush method, it will allow for a more rapid and slightly more reliable test, however, it will also result in many more women facing the worry of being called back for more detailed examinations, where no abnormality will be found (a so-called ‘false positive’). The transition to this new testing process will have to be accompanied by better education of medical professionals and the public in general, if we are to ensure empowerment of women to improve their health with such advances.

No screening technology will eliminate cervical cancer risk, however, screening goes hand-in-hand with vaccination to allow, for the first time, for the possibility of the effective elimination of this form of cancer within our lifetime. Knowledge that cervical cancer is caused by viruses, has allowed for the development of a safe and effective vaccination strategy. By ensuring that all males as well as females receive a vaccination prior to HPV exposure, we will protect all future sections of Irish society from getting the virus in the first place.

With 300,000,000 doses of the vaccine delivered, over more than a decade, across the globe, we know that this vaccine is safe with the only major side effects, being a sore arm and occasional fainting. The current vaccine effectively protects against 7/10 cases of cancer-causing HPV (this will rise to 9/10 with a new variant of the vaccine) and such a high protection rate coupled with ongoing monitoring with HPV-based cervical screening will ensure that cervical (and other HPV cancers) can be effectively eliminated from our lives.

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