Human Papillomavirus and Cancer

Human Papillomavirus (HPV)

The human papillomavirus, or HPV, is a type of virus that infects the skin and the cells lining body cavities. For most people, the infection will get better on its own and they will never know they had it. 

There are different types of HPV:

Some infect the skin, usually on the fingers and hands. These can cause minor problems, such as common skin warts and verrucas.

Others infect the genitals, mouth and throat. These can cause genital warts, or more rarely, cancer.

From this point onwards, the discussion is on genital and oral HPV, as these types are the ones which can cause cancer.

HPV is a very common infection. Around 8 out of 10 people will be infected with the virus at some point in their lives. It usually doesn’t cause any symptoms and most people will never know they had it. HPV spreads through close skin-to-skin contact, usually during sexual activity including oral sex. Having a high number of sexual partners does increase the chances of infection. 

HPV infection usually causes no problems at all. But in some people the infection will stay around for a long time and become persistent. Around 13 types of HPV can cause cancer. These are called ‘high-risk’ types. People with persistent infections with ‘high-risk’ HPV types are those who are most likely to go on to develop cancer.

HPV & Cancer

The main type of cancer linked to HPV infection is cervical cancer. Virtually all cases of cervical cancer are caused by HPV. About 3,100 cases of cervical cancer are diagnosed in the UK each year.

HPV can also cause cancer in other genital areas, like the vagina, vulva, penis, and anus. It can also cause some types of cancer of the mouth and throat.

The majority of vaginal, vulval, penile and anal cancers are caused by HPV. But they are less common than cervical cancer. Men who have sex with men may be at increased risk of anal cancer.

HPV infection also increases the risk of some types of mouth and throat cancers. Rates of mouth cancer, especially tongue and tonsil cancers, are on the increase, particularly in people in their 40s, 50s and 60s.30–34 And the evidence suggests that the proportion of cases linked to HPV is rising.

How HPV leads to Cancer

HPV can cause cells to divide more than usual. Fast cell growth can cause warts to develop, but often it doesn’t cause any symptoms at all. The types of HPV that cause warts are not the same types that cause cancer.

In persistent ‘high-risk’ HPV infections, the virus can damage DNA and cause cells to start dividing and growing out of control. This can lead to cancer.

HPV Vaccine

HPV can cause changes to the DNA in our cells that make them more likely to turn cancerous. So by protecting against HPV infection, we can help prevent those changes and reduce the risk of cervical cancer.

HPV Vaccination for Women

Since 2008, girls aged 11-13 have been offered a vaccination against the two most common ‘high-risk’ types of HPV, HPV 16 and 18. Together, these two types cause about 7 out of 10 cervical cancers. Girls up to the age of 18 can request vaccination through the NHS if they weren’t vaccinated routinely. The HPV vaccine has been proven to be safe and effective.

The HPV vaccine currently used in the UK (Gardisil) also protects against HPV 6 and 11, which are the HPV types that cause most genital warts.

The HPV vaccine doesn’t protect against all types of HPV, so screening is still important, even if you have been vaccinated.

HPV Vaccination for Men

As HPV is linked to cancers in men as well as women, offering HPV vaccination to men would help reduce the risk of disease. Men who have sex with men have a higher risk of anal cancer than men who don’t.

From April 2018, the vaccine is being rolled out men who have sex with men in all sexual health and HIV clinics across the UK.

The Joint Committee for Vaccination and Immunisation are also currently considering whether to offer HPV vaccination to all teenage boys as well as girls.

Cervical Screening for HPV

Cervical screening aims to pick up early cell changes that are caused by HPV and remove these cells before they have a chance to become cancerous. This is done by taking a sample of cells and sending them to a lab where they are tested to see if they are normal (cytology). If the cells look abnormal, they will be tested for HPV to see if they are more likely to become cancerous. If they test positive for HPV, the cells will be removed.

Source: https://www.cancerresearchuk.org/about-cancer/causes-of-cancer/infections-hpv-and-cancer/hpv-and-cancer

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Chlamydia Infection May Pave Way For Cancer via DNA Damage

The bacterium Chlamydia trachomatis is a leading cause of sexually transmitted disease that infects over 90 million people worldwide every year. Chlamydia infection often goes unnoticed, can persist for years with little or no symptoms, and can damage women's reproductive organs.

As well as this, the bacterium is proving increasingly stubborn to shift: antibacterial drugs are often no longer strong enough to eradicate it completely, so it goes into persistent mode, leading to chronic infection with no symptoms.

Chlamydia Uses Various Tactics to Ensure Survival

Chlamydia uses "Trojan horse" tactics to enter host cells unnoticed. A protein called Pgp3 enhances Chlamydia's ability to enter host cells unnoticed and then evade host defences.

To ensure survival, Chlamydia needs to make the most of the resources inside the host cell, which is where the bacterium spends most of its life. Once inside the host cell, the pathogen goes about changing the cell to make itself at home. It re-arranges host cell processes to favour its own growth and proliferation. But it's not clear how this affects the cell's normal functions and whether it leads to disease.

However, there is evidence that it might: there is a growing mountain of epidemiological data linking Chlamydia infections to the development of cervical and ovarian cancer development. But exactly how this might come about has been somewhat of a mystery - until now.

Chlamydia Causes Lasting Genetic Damage to Host Cells

In this new study, the researchers show that Chlamydia makes a long-lasting impression on the genome and epi-genome of host cells. Such changes are increasingly implicated in the development of a range of cancers.

They found host cells acutely and persistently infected with Chlamydia had increased levels of different kinds of DNA breaks.

In normal cells, when these types of breaks occur, they either go into cell suicide mode (apoptosis, where the cell is removed, broken down and its material parts recycled) or DNA repair mode.

In DNA repair mode, special proteins trigger a process called DNA Damage Response which attempts to reseal the broken strands of DNA to make sure the correct sequence of genetic code is restored (so when the cell replicates it produces healthy daughter cells).

But not only did the researchers find that Chlamydia-infected cells had altered DNA, but also that their DNA Damage Response didn't work properly: so the broken DNA didn't get repaired in those cells that didn't go down the cell suicide route.

Chlamydia disrupted the host cell DNA Damage Response by stopping key proteins from reaching the sites of DNA damage.

Chlamydia Damage to Cells Is Similar to that Which Leads to Cancer

Thus Chlamydia-infected, damaged cells that did not go down the cell suicide route continued to proliferate, passing on the DNA damage, and also spurred by some extra pro-survival signals activated in the host cell by the pathogen.

The result is an increasing population of rogue host cells that have escaped the normal mechanisms that ensure faulty DNA is not replicated: a hallmark of cancer.

The discovery is important because if it is established that an infection leads to cancer, then vaccination to prevent the infection, or antibiotics to eliminate it, may also prevent the cancer.

Such preventive methods are already working with other cancer-causing agents such as Human Papilloma Virus (HPV) and Helicobacter pylori, which can cause cervical and gastric cancer, respectively.

However, the path from infection to cancer needs to be firmly established before such a strategy can be considered in the case of Chlamydia.

Source: https://www.medicalnewstoday.com/articles/262350.php

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