Cancer patients are three times more likely to think they would be "better off dead" or to contemplate suicide than the rest of the population - a Cancer Research UK study reports online today.
Patients were most likely to have these thoughts if they had substantial pain and particularly if they had serious emotional distress.
The study highlights the need for more support services to be available for cancer patients and that this is particularly important in the area of pain management.
Almost 3,000 outpatients took part in the study at the Edinburgh Cancer Centre.
The patients, who had a range of cancers, answered a computerised questionnaire about their physical and emotional symptoms.
Among the questions, patients were asked: "Over the last two weeks how often have you been bothered by the following problem: thoughts that you would be better off dead, or of hurting yourself in some way?" Patients could answer: "not at all," "several days," "more than half the days" or "nearly every day."
Of the 2,924 patients who took part, nearly 8 per cent said they had thoughts of being better off dead or of hurting themselves. This compares with a figure of just 2.6 per cent in a similar survey of the general population conducted in Australia.
Lead author Jane Walker, based at the Edinburgh University, said: "It is worrying that, despite improvements in cancer care, a substantial number of patients feel they would be better off dead.
"We know that depression is common in patients who have cancer but it is often missed. Pain is also a big problem. Treating patients' symptoms as well as their disease might improve, and even save, their lives."
Dr Lesley Walker, Cancer Research UK's director of cancer information, said: "It is normal to experience distress after a cancer diagnosis. But for some patients emotional distress or depression becomes a problem in itself and may lead to suicidal thoughts. Cancer specialists and GPs can provide treatment, with the help of psychiatrists if necessary."