When mice are exposed to chronic, ongoing stress, their lymphatic systems undergo physical changes that make it quicker and easier for cancer to spread throughout their bodies, researchers have found.
Although the study hasn't been replicated in humans as yet, it's a huge step towards understanding how stress - which has long been linked to cancer progression - actually helps tumour cells escape. But more importantly, the researchers have already found a drug to stop this from happening and are now testing it in women with breast cancer - so don't worry, no one's going to be telling you to 'relax' your way through cancer.
"Not for a minute are we suggesting that someone who's just been diagnosed with cancer should not be stressed, because that would have to be one of the most stressful situations," one of the researchers, Erica Sloan from Monash University in Australia, told ABC News. "But rather how do we look after cancer patients, because this suggests that stress not only affects patient wellbeing but also gets into the body and affects how the tumour progresses."
There are two ways that cancer spreads throughout the body - through the blood vessels or through the lymphatic system, which is a network of tubes that drain fluid from tissue back into the bloodstream. But once it's out, it can form deadly secondary tumours, which is why it's so important for doctors to remove cancer as quickly as possible once it's detected.
Scientists already know that stress hormones can increase blood vessel formation, giving cancerous cells more potential escape routes, but until now it wasn't clear whether they also influenced the lymphatic system.
To figure that out, the team restrained mice to put them under extreme stress, which the researchers compare to someone feeling like they just can't cope with their circumstances for a long period of time - for example, if they're caring for a sick relative without enough resources (we're not talking about the stress of a single bad day in the office here).
They found that the stressed-out mice had a higher rate of cancer spreading than their relaxed peers, and were able to show that this was because the stress hormone adrenaline was activating the sympathetic nervous system (SNS) to up the rate of lymph formation.
Not only that, the stress hormone actually physically changed the lymph vessels draining out of tumours, allowing cancerous cells to escape to other parts of the body faster.
"So not only do you get new freeways out of the tumour but the speed limit is increased and so the tumour cells can flow out of the tumour much more rapidly," said Sloan.
You can see that happening below, with the top lymph vessel unaffected by stress, and the bottom lymph vessel under chronic stress. That little white circle reflects a particle, such as a potential tumour cell:
But here's the good news - the researchers were able to use a beta-blocker called propranolol, which is already on the market, to stop this from happening.
And seeing as propranolol has already been used for years around the world, the researchers took things one step further and looked back at human studies to see if there was any indication that beta-blockers could have unknowingly been slowing the spread of cancer this whole time.
After reviewing data on nearly 1,000 breast cancer patients in Italy, they found some pretty compelling results. "When tracked over about seven years, it turned out that those that had been taking beta-blockers also showed far less evidence of tumour cells moving into the lymph nodes and then disseminating to other organs like the lung, so it provides clinical support for what we see in the mice," Sloan told ABC.
The researchers are now conducting a pilot study in Melbourne using propranolol in a group of women with breast cancer, and we really hope it works, because having a cheap and easy way to reduce the risk of cancer spreading would be a huge win.
The research has been published in Nature Communications.