Cancer patients often struggle with depression
Depression can damage a cancer patient's chances of survival, a review of research suggests.
The University of British Columbia team said the finding emphasised the need to screen cancer patients carefully for signs of psychological distress.
The study, a review of 26 separate studies including 9,417 patients, features in the journal Cancer.
It found death rates were up to 25% higher in patients showing symptoms of depression.
In patients actually diagnosed with major or minor depression, death rates were up to 39% higher.
The increased risks remained even after other clinical characteristics that might affect survival were taken into consideration.
However, the researchers said more research was needed before any definitive conclusions could be drawn, as it was difficult to rule out the impact of other factors.
They also stressed that, overall, the increased risk of dying from cancer due to depression was small - so patients should not feel they had to maintain a positive attitude to beat their disease.
The studies looked at by the British Columbia team focused on a range of survival times, from one year to 10 years.
The researchers could find no firm evidence to show that depression impacted on the progression of disease - although the number of studies which specifically looked at this was very limited.
Research on animals has suggested that stress can have an effect on tumour growth and the spread of cancer to other parts of the body.
It is possible that depression could have an impact on hormones or the immune system, or that depressed people tend to engage in behaviour which might affect how long they live.
For instance, depressed people may be less likely to comply with treatment regimes.
However, at this stage there is no firm proof that depression actually causes cancer patients to die earlier than they otherwise would.
Previous research has suggested that depression has a much bigger impact on mortality from heart disease.
Lead researcher Jillian Satin said: "It is quite remarkable that the presence of depressive symptoms or a diagnosis of a depressive disorder can predict mortality in cancer patients.
"But it should be kept in mind that the increased risk is quite small.
"Cancer patients need not panic if they are experiencing depressive symptoms, but it is certainly reasonable to talk to their physicians about their mental health."
Dr Julie Sharp, of the charity Cancer Research UK, said: "This research adds weight to the importance of identifying depression early in people with cancer and offering them appropriate support and care."
But she added: "There are still many unanswered questions as the effects observed in this study are quite small and may be due to other factors.
"More research will be needed to explain whether these observations are true and if so why."