
Immune cells (white). Image courtesy of LRI EM Unit. Immune cells found in the blood.
This entry is part 13 of 23 in the series Science Surgery
Our Science Surgery series answers your cancer science questions.
Millie asked us on Instagram: “Why doesn’t the immune system attack cancer cells?”
“Our immune system does attack cancer cells,” says Professor Tim Elliott, a Cancer Research UK-funded immunologist from the University of Southampton.
“It’s recognising and destroying little cancers as they develop all the time. If we didn’t have an immune system, then we would be developing cancer a lot more often.”
This is because the process of cell division isn’t perfect. The rate at which some cells grow and divide means errors can happen and cells become damaged.
In most cases, our immune system acts as quality control, making sure these cellular mistakes are nipped in the bud before they become too sinister. A group of immune cells, called killer T cells, are the ones mostly responsible for patrolling our bodies and destroying damaged cells or small tumours before they cause us harm.
So, if our immune system is so good, why do we still develop cancers that need treatment?
Immune cells eliminate tiny tumours
In the very early stages of cancer our immune cells do a good job of killing individual cancer cells as they arise. This is known as the ‘eliminating phase’, where immune cells are in control of the tumour and calmly carry out their work.
“However, if the rate of tumour growth begins to match the activity of our immune system then we enter a stage of equilibrium,” says Elliott.
Here, the immune cells are doing a good enough job at staying on top of cancer cells as they grow and divide, even though their workload is increasing.
“Some tumours can actually get fairly big but still be kept in check by our immune cells,” says Elliott. “This behaviour can sometimes last for several years.”
But as time goes on, cancer cells can develop genetic changes that help them escape the immune system. This is what has been called the ‘escape phase’.
“Unfortunately, once cancer cells really start to change and grow, they come up with ingenious ways of bypassing our immune cells and escaping their detection.”
It’s at this point that immune cells can’t keep up with the evolving tumour. Some cancer cells in the tumour become too clever and immune cells can’t adapt fast enough to keep them at bay.
Escaping the immune system
Immune cells recognise danger through a group of molecules found on the surface of all cells in the body. This helps them inspect potential problems closely and decide whether to attack.
But when a cancer reaches the ‘escape phase’ it can change. The molecules that would otherwise reveal the cancer to the immune system are lost, and killer T cells move past, unaware of the danger the cancer cell could cause.
“That’s a sure-fire way of escaping detection,” says Elliott, adding that it’s one of many escape methods cancer cells use.
“Cancer cells also develop ways to inactivate immune cells by producing molecules that make them stop working.” They also change their local environment, so it becomes a hostile place for immune cells to work.
“Once the tumours have changed their environment, any circulating killer T cells that arrive in this space are rendered inactive,” says Elliott.
Upskilling immune cells
Research has shown that changes to immune cells don’t need to be permanent. The theory is that if there’s a way to reverse these tricks, or stop immune cells falling for them, their cancer-fighting ability could be restored.
This has formed the basis of a growing range of cancer treatments called immunotherapies. And for some cancers, these drugs offer the chance of a cure that would’ve been impossible a decade ago.
They can work by releasing the brakes on immune cells so they can get cancer cells back in line. And a group of these drugs, called checkpoint inhibitors, are now being routinely used to treat a range of cancers, including some melanomas, lung and kidney cancers.
But these drugs don’t work for everyone. And scientists still need to understand more about how cancer cells get the better of immune cells. Pinpointing how cancer cells move from the ‘eliminating phase’ towards ‘escape’ could uncover new ways to stop this from happening.
So we should be reassured by the immune system’s ability to keep damaged, rogue cells at bay.
And when this ability dwindles, research is leading to immunotherapies that can reenergise our immune cells and get cancer back under control.
Gabi
We’d like to thank Millie for asking this question. If you’d like to ask us something, post a comment below or email [email protected] with your question and first name.
- Introducing our Science Surgery series
- Science Surgery: ‘What factors lead to a cell becoming cancerous?’
- Science Surgery: ‘Could more cancers be caused by inherited faulty genes than we now think?’
- Science Surgery: ‘Will cancer ever be cured?’
- Science Surgery: ‘Is the one-size-fits-all treatment approach obsolete?’
- Science Surgery: ‘Does having had cancer make you more likely to develop it again?’
- Science Surgery: ‘What’s being done to use treatments in different types of cancer?’
- Science Surgery: ‘Do we all have potentially cancerous cells in our bodies?’
- Science surgery: “What’s the difference between the words genome, gene and chromosome?”
- Science Surgery: ‘Will cancer ever be eradicated completely?’
- Science Surgery: ‘How quickly do tumours develop?’
- Science Surgery: ‘Why do never-smokers get lung cancer?’
- Science Surgery: ‘Why doesn’t the immune system attack cancer cells?’
- Science Surgery: ‘How do tumours ‘know’ where to spread?’
- Science Surgery: ‘How is skin cancer related to sun exposure?’
- Science Surgery: ‘Does cancer attack every age group?’
- Science Surgery: ‘Why do some cancer treatments stop working after so long?’
- Science Surgery: ‘Does cancer affect the future development of children?’
- Science Surgery: ‘How do cancer cells remain dormant for many years?’
- Science Surgery: ‘Why do some cancers metastasise, but others don’t?’
- Science Surgery: ‘Are benign tumours different from cancerous tumours?’
- Science Surgery: ‘How are children’s cancers different from adults’ cancers?’
- Science Surgery: ‘Can cancers develop in the heart?’
Comments
Katie Roberts June 12, 2019
Thanks to everyone who has submitted a science surgery question, we really appreciate your interest. We can’t answer every question we receive, but make sure you follow the series on our blog to keep an eye out for those we do. We can’t give medical advice on individual cases, but If you would like to speak to one of our nurses please call them on freephone 0808 800 4040.
Katie, Cancer Research UK.
Norma Watson May 9, 2019
Very thorough explanation to the above question. I rarely get a cold so thought my immune system would be able to deal with anything, unfortunately not this. Is there any way of testing the capabilities of one’s immune system?
Maureen March 10, 2019
You do not mention once about nutrition and how to maintain a healthy immune system through diet, why is that? Eating plant based foods are proven to do this, so surely you should be promoting better eating habits.
Tricia Bowler March 10, 2019
Interesting article. Thankyou. I have had two types of cancer. and wonder why when I keep weight down, exercise and eat properly.
Angela Baldwin March 9, 2019
Do Cyst always develop into a tumour?
Dave Shone March 8, 2019
Your answer to the question “Why doesn’t the immune system attack cancer cells?” was very comprehensive and gave some useful links to more, in depth, information on the subject. Having been involved in cancer research myself, I am most impressed by your website.
Behzad Nili March 1, 2019
What do you expect if just one class of drugs NSAIDs block almost 35 important local hormones which after 3 minutes of action are destroyed when you block all of them it’s obvious that there’s somehow a predictable response and that’s messing up with the entire physiology including the immune system but it’s unpredictable because there are so many things messed with
Sandra August 15, 2019
This site is very helpful and.informative