A survey of more than 21,000 patients in Scotland found rates of clinical depression ranging from six per cent to 13 per cent, compared with a prevalence of just two per cent in the general population. Of the 1,130 who had been diagnosed, almost three quarters (73 per cent) were not receiving any kind of effective treatment.
The findings were revealed as doctors reported promising results from two trials testing a new approach to managing depression in cancer patients.
SMaRT (Symptom Management Research Trials) Oncology 2 and 3 used specially trained nurses to deliver a range of psychiatric care including behavioural therapies and medication.
Professor Michael Sharpe, from Oxford University, one of the researchers whose findings are reported in the journal The Lancet Psychiatry, said: "Major depression is really quite common in people with cancer and the perhaps surprising finding is that most of it goes untreated. The outcome with usual care is poor.
"We've described a new approach to managing depressed cancer patients that is based on the shortcomings of usual care and integrated with cancer care that really has quite spectacular effects in the good prognosis patients and also has efficacy in the poor prognosis patients."
Speaking at a press conference in London, he added: "People are often knocked flat by cancer and cancer treatment.
"What this programme does is get people back engaged with life and feeling more in control of their lives again.
"One of the biggest barriers we have to overcome is people thinking being depressed is part and package of cancer."
In the first of a series of three papers, the researchers outlined findings from data on 21,151 men and women with lung, breast, bowel, genito-urinary (including prostate and bladder) or gynaecological cancers.
All of the patients had participated in routine screening for depression in Scottish cancer clinics between May 2008 and August 2011.
Those with lung cancer had the highest prevalence of major depression (13.1 per cent) followed by patients with gynaecological cancers (10.9 per cent) and breast cancer (9.3 per cent).
Seven per cent of patients with bowel cancer were seriously depressed, as were 5.6 per cent of individuals with genito-urinary cancers.
At the time of screening, 73 per cent of 1,538 patients diagnosed with depression were not receiving "potentially effective" therapy for their mental state.