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Does stress cause cancer?

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Stress “could cause cancer”, according to The Daily Telegraph. The newspaper says that research in fruit flies provides evidence that “everyday emotional stress is a trigger for the growth of tumours”.

This story is based on complex research in fruit flies that found that cells carrying different genetic mutations can interact to cause the growth of tumours. Although the researchers refer to “stress” in one small part of their study, they are referring to the biological strain cells and tissues experience under unfavourable conditions such as when tissue is damaged.

The research may give us clues as to how human cancer cells interact, but cannot tell us anything about whether everyday emotional stress can cause cancer in humans. Minimising stress improves emotional wellbeing. One way to minimise stress is to avoid reading news stories that cause unnecessary health worries

Where did the story come from?

Dr Ming Wu and colleagues from Yale University School of Medicine in the US and Fudan University in China carried out this research. The study was funded by the National Institutes of Health and National Cancer Institute in the US. It was published in the peer-reviewed scientific journal Nature.

This study has also been reported by the Daily Express and Daily Mirror.  The publications either suggest that psychological/emotional stress can cause cancer, or fail to make it clear what kind of “stress” the research actually looked at.

What kind of research was this?

This was an animal study in fruit flies looking at how cells carrying different mutations interact and affect the growth and spread of tumours. Human tumours are thought to contain a variety of different cells that may carry a number of different genetic mutations. The way a tumour progresses is thought to be affected by the interactions between these different cells and the environment around them.

Fruit flies were used in this study because scientists have now developed genetic techniques that allow them easily to look at the interactions between cells carrying different mutations in flies. Although there are similarities between flies and humans on a cellular level, there are also differences. Looking at tumour growth in fruit flies may provide clues about what occurs in human tumour cells, but research using human cells would be needed to confirm this.

What did the research involve?

The researchers were looking at two mutations: one called RasV12 that promoted tumour growth and one that blocked the action of a gene called scribbled, that usually suppresses tumour growth. Fruit fly cells that carry just the RasV12 mutation divide more than usual, and cells that carry the scribbled mutation usually die. However, cells that carry both mutations develop into large metastatic tumours.

The researchers wanted to see what would happen if cells carrying the RasV12 mutation grew next to cells carrying the scribbled mutation. In particular, they wanted to see whether these cells could work together to cause a tumour to grow and spread into neighbouring tissues. They also looked at how the cells interacted and signalled to each other.

In order to test these theories, the researchers genetically engineered fly larvae to carry either the RasV12 or scribbled mutation in the cells of their developing eyes. They also carried out a number of complex experiments to look at how cells carrying these mutations might work together.

What were the basic results?

The researchers showed that when cells carrying the RasV12 mutation were next to cells carrying the scribbled mutation they caused large tumours to grow and spread into nearby tissue. The researchers investigated how these cells might interact and identified important components of the biochemical pathways involved . One of the effects triggered by the scribbled mutation is also known to be triggered by ‘biological stress’, for example due to tissue damage. The researchers found that damaging tissue that carried the RasV12 mutation could also promote cells to divide more, but did not cause them to spread.

How did the researchers interpret the results?

The researchers say that their findings in fruit flies highlight the importance of cell interactions in “oncogenic co-operation and tumour development”. They also suggest that this type of co-operation between cells with different mutations could play a role in the development of human cancers.

Conclusion

This complex research has found that cells carrying different mutations can interact with each other and cause tumours to grow and spread in fruit flies. This is interesting because it is generally thought that the mutations have to occur in the same cell in order for tumours to develop.

On the level of individual cells, there will be a lot of similarities between fruit flies and other species, but there will also be differences. For this reason, these results may suggest what might occur in human tumours, but only research in human cells can confirm this.

Several newspapers seem to have missed the point of this research, with some suggesting that it shows a carcinogenic effect from emotional stress. While the researchers refer to stress in one small part of their study, they are talking about biological stress seen in cells and tissues under unfavourable conditions, for example, in this case the researchers caused biological stress to cells by damaging the developing eye tissue.

Overall, this research has identified a biological mechanism that can lead to the formation of tumours in fruit flies. The findings of this research may in turn lead to studies in human cells, but do nothing to inform us about how emotional stress might be related to the risk of cancer.

Links to the headlines

Stress could cause cancer claim scientists. The Daily Telegraph, January 14 2009

Stress cells’ cancer link. Daily Mirror, January 14 2009

Stress ‘may cause cancer’. Daily Express, January 14 2009

Links to the science

Wu M, Pastor-Pareja JC, Xu T. Interaction between RasV12 and scribbled clones induces tumour growth and invasion. Nature, January 13 2009

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