Have fun and will survive cancer tumours, at least in mouse model. And some mild stress, a stimulating milieu, too could help. The study led by a New Zealand neuro-scientist seems to confirm the belief that mental states play an important role in cancer.
"The way we live may well have a much bigger impact on the prognosis of cancer than we recognized previously," said Professor Matthew During, of Auckland University and Ohio State University in the US.
Lifestyle changes, especially doing more physically and socially challenging activities like team sports or social activities involving some competition and mild stress, could have positive consequences for cancer patients, the team showed.
The findings, published in the journal Cell, point to a possible neurological treatment for cancer.
Dr. During's team injected mice with melanoma, a type of fast-growing skin cancer, and let the tumors grow. They put some of the mice in a large cage, with lots of toys, space and many more other mice than usual.
Other mice stayed in ordinary lab cages.
After three weeks, tumors shrank almost in half in the mice in the "stimulating" cage and they shrank 77 per cent after six weeks. The tumors completely disappeared in 17 per cent of the mice, with no other cancer treatment.
Tumors continued to grow in the other mice.
Dr. During believes that more than simple stimulation is at work in the mice. The mice in the "enriched" cages were a little stressed out.
"You find some of them with little bite marks and fight marks," said Dr. During. "It's not all friendly."
Although common wisdom holds that stress is not healthful, the body's response to stress is complex, and hormones released in response to stress can have positive effects.
To show the benefits were not simply due to exercise, the researchers placed running wheels in the smaller cage. The mice ran up to three times as far as the mice in the large cage, but were not more resistant to cancer.
Changes were found in the "enriched" group's immune systems and in the levels of a number of hormones, the most dramatic being the reduction in leptin - an appetite regulator - released from fat cells.
"There's a link between cancer and obesity. This is the first definitive proof that leptin mediates the cancer effect. We describe here a specific pathway of how the brain talks to fat to reduce the release of this hormone," Professor During told New Zealand Herald.
In this study, extra copies of a gene involved in weight regulation, BDNF, were implanted in the "less-stimulated" group, leading to 75 per cent tumour shrinkage.
He has previously established that BDNF implants reduce obesity in animals. He is trying to set up trials for severely obese humans and can now see benefits in extending this to obese cancer patients.
The research could lead to new ways of tackling cancer and perhaps other diseases, said the scientists. This could either involve exposure to mentally or socially stimulating environments, or a drug that mirrors the same effect.
An important avenue for further studies would be to find out how to boost BDNF in humans, said Prof During.
He added: 'We're really showing that you can't look at a disease like cancer in isolation. For too long, physicians and others have stuck to what they know - surgery, chemo, radiotherapy.
'Traditionally working on the area of lifestyle and the brain has been a 'soft area'. This paper really suggests if we look at people more in terms of their perceptions of disease, their social interactions and environment, we could realise a profound influence on cancer. There's no reason to suspect our findings (in mice) won't be generalisable.'
The New Zealand Cancer Society said people being treated for cancer had to be realistic about what activities they could maintain, because of fatigue and other physical effects.
Pressure to continue with usual social and work activities could add more stress, but retaining as much normality as possible could be beneficial. The society encourages patients to maintain their social and work connections to the extent possible.