It’s a controversial question that has long divided the world’s leading scientists: can stress cause cancer?
For years, physicians treating their patients have frequently observed that serious life events (losses, divorces, and major traumas) often occur in the years immediately preceding the onset of the illness.
However, the actual evidence is far from conclusive. Even Cancer Research UK (CRUK) says the links are not only unproven, but may be little more than a myth.
But with stress levels on the rise and an estimate that the number of people with cancer will rise by a third to four million by 2030, some cancer experts now say emerging evidence about the impact of stress on the body means it would “not be surprising” if there was a link between the two.
Professor Melanie Flint, from the University of Brighton, who studies the impact of stress hormones on cancer, said: ‘There is a lot of progress in this field and I don’t think we can rule out the contribution of stress to cancer.
For years, doctors treating patients have often observed that serious life events (bereavements, divorces and severe traumas) usually occur in the years immediately preceding the onset of the disease (archive image)
“In my opinion, it does contribute, both to the onset of cancer in the first place and to its spread once you have it, but it is a contributing factor, not necessarily a direct cause.”
Some studies that have followed large populations over time seem to support this.
A study of 10,000 women in Finland, followed for 15 years, found that those who had suffered losses were more likely to develop breast cancer within five years.
Exposure to workplace stress has been associated with an increased risk of prostate cancer in men under age 65 and, although the link was weaker, with breast cancer in women.
However, other similar studies – including higher-quality evidence reviews – fail to show any association.
Part of the problem, according to Professor Trevor Graham, director of the Centre for Evolution and Cancer at the Institute of Cancer Research, is that stress often goes hand in hand with other behaviours that also increase cancer risk.
“A stressful life can be interrelated with many other cancer risk factors, such as smoking, drinking too much alcohol, inactivity and an unhealthy diet, so it is difficult to separate causal factors,” she says.
What we do know is that stress causes a cascade of effects on the body, especially if it is chronic.
Professor Flint says: ‘Stress triggers the release of the stress hormone cortisol.’
‘Cortisol binds to receptors found on every cell and regulates several other processes, including inflammation.
‘Stress and cortisol can also suppress the immune system.’
Scientists have also attempted to mimic the effect of stress on cells in the lab, which appears to show that it damages DNA and causes changes in cells that, if allowed to replicate, can develop into cancer.
But because stress is difficult to model, this may not be a good indicator of what is actually happening in the human body, Professor Graham points out.
It is also likely that most people can repair this damage naturally.
But there is one notable exception: those with genetic mutations that already put them at higher risk of cancer – such as those with the “Angelina Jolie” genes BRCA1 and BRCA2, named after the Hollywood actress who inherited them from her late mother, who died of the disease – may be less able to do so, says Professor Flint.
“If someone has a cancer mutation that affects the ability to repair DNA, such as BRCA, they may be more vulnerable to the effects of stress,” she says.
“We can’t say that if you are very stressed and have a cancer mutation, you will definitely develop cancer. We don’t yet fully understand all the underlying mechanisms.
“But we may need to consider it as a potential additional risk for some people and stress management may be necessary.”
There is also some limited evidence, she adds, that stress may indirectly increase the risk of developing cancer by triggering the emergence of viruses such as human papillomavirus (HPV), which is linked to cervical cancer.
However, where the evidence is strongest, it suggests that stress may play a role in causing cancer to spread once it has already developed.
Professor Nazanin Derakhshan from the University of Reading said: ‘In breast cancer there is evidence that anxiety and depression increase the risk of recurrence and mortality.
“There are more and more studies reporting this and we cannot ignore it.”
Professor Flint says cortisol may help cancer cells evade the immune system and spread from the original tumour site to a secondary site.
‘If you are stressed and this has weakened your immune system, or stress hormones are acting on the cancer cells themselves, then the cancer cells can hide from the immune system and, depending on the type of cancer, spread to harder-to-treat areas such as the brain, lungs, bones and liver.
‘While the evidence on whether stress can cause cancer may be unclear, it is much clearer that it can cause an existing cancer to spread.’
More evidence is likely on the horizon.
Oncologist Professor Charles Swanton, CRUK’s clinical director, said: “Over the next five to ten years, we may start to see data emerge proving the link between stress and cancer.”
But in the meantime, people who already have cancer, or those with a genetic mutation that increases their risk, should get help to manage their stress levels, Professor Flint suggests.
This could involve talking therapies, medication, exercise, or simply “taking care of yourself” – all of which will be good for you whether you have cancer or not.