Vaccines are medicines that help the body fight disease. They can train the immune system to find and destroy harmful germs and cells. There are many vaccines that you receive throughout your life to prevent common illnesses. But why aren’t there vaccines for prostate cancer?
Your immune system is your body’s natural defence system. Vaccines work by teaching your immune system to recognise things that don’t belong in your body. Your immune system can recognise these germs because they are coated in proteins and sugars (known as antigens) that don’t match any in your body. When you have a vaccine, it trains your body to recognise these unusual coatings, and your immune system develops a ‘memory’ of what the infecting germ looks like. This means that if you come into contact with a disease, your immune system can fight it off before you even get ill!
Watch a useful animated video showing how vaccines work:
Vaccines videoCancer vaccines can be split into two main types:
Some cancers are caused by viruses. Scientists have developed vaccines that can prevent healthy people from getting the cancers caused by these viruses. Like vaccines for the chicken pox or the flu, these vaccines protect the body from these viruses. This type of vaccine will only work if a person gets the vaccine before they are infected with the virus.
The important thing here is that the vaccine is against a virus, NOT against cancer.
Hepatitis B virus (HBV)
People who have chronic (long-term) infections with HBV are at higher risk for liver cancer. Getting the vaccine to help prevent HBV infection may lower some people’s risk of getting liver cancer.
Human papillomavirus (HPV)
HPV is the name given to a very common group of viruses. There are many types, some of which are “high risk” because they are linked to causing cancers, such as cervical, anal, throat, vaginal, vulvar, and penile cancers. In fact, infection with this virus is responsible for more than 99% of cervical cancers. Vaccinating children and certain young adults against HPV helps protect against cervical cancer and the other five cancers HPV can cause.
These are traditional preventive vaccines that target the viruses causing the cancer. They may help protect against some cancers, but they don’t target cancer cells directly because cancer cells have not yet been formed or found.
Therefore, these types of vaccines are only useful for cancers known to be caused by infections. But most cancers, including prostate, colorectal, lung, and breast cancers, are not thought to be caused by infections.
There are vaccines in development that treat existing cancer, called treatment vaccines or therapeutic vaccines.
Cancer treatment vaccines are different from the traditional vaccines that work against viruses and other diseases. These vaccines don’t boost the immune system to help prevent a disease, but instead boost the immune system to help it fight cancer cells already in the body. Doctors give treatment vaccines to people who already have cancer.
Treatment vaccines work in the same way that the traditional preventative vaccines do. The vaccines are made to recognise antigens (the proteins and sugars that coat cells) that are on the surface of particular cancer cells. These are called cancer-specific antigens because healthy cells do not have them.
When a cancer vaccine gives these antigens to a person, they tell the immune system to find and destroy the cancer cells that have these molecules on their surface.
How do treatment vaccines work?
Different treatment vaccines work in different ways. They can:
Vaccines are often combined with other substances or cells called adjuvants that help boost the immune response even further.
Cancer vaccines cause the immune system to attack cells with one or more specific antigens. Because the immune system has special cells for “memory” which remember the antigens your body has fought against, it is hoped that vaccines may continue working for a while after they are given.
There are currently no vaccines available for prostate cancer on the NHS. Why is this?
Cancer is personalised. First and foremost, cancer is not a virus, bacteria or even a single disease. It is a group of many different diseases. Every single cancer is unique; a prostate cancer in one person is completely different to a prostate cancer in another person. Tumours within the same person may even be made up of very different cancer cells. This makes it an extremely complicated thing to treat.
Cancer cells suppress the immune system. This is how cancer is able to begin and grow in the first place. Vaccines rely on an immune response to work. Researchers are using adjuvants in vaccines to try to fix this problem.
Knowing what to target. Many cancers are caused by not one, but many, gene mutations working together, so developing a vaccine to target all possible mutations is likely impossible. Instead, researchers are trying to target more common mutations and antigens.
Cancer cells start from a person’s own healthy cells. As a result, the cancer cells may not “look” harmful to the immune system. That’s why, even when the immune system is stimulated by certain drugs, it doesn’t always know what cancer targets to attack. The immune system may ignore the cells instead of finding and fighting them.
Larger or more advanced tumours are hard to get rid of using only a vaccine. This is one reason why, when a cancer vaccine is available, doctors often have to give it along with another treatment.
People who are sick or older can have weak immune systems. Their bodies may not be able to produce a strong immune response after they receive a vaccine. That limits how well a vaccine works. Also, some cancer treatments like chemotherapy, weaken a person’s immune system. This limits how well the body can respond to a vaccine.
For these reasons, some scientists think cancer treatment vaccines may work better for smaller tumours or cancer in its early stages. It is harder to develop drugs for early stage cancers, because the greatest need is when cancer is advanced stage.