Large numbers of cancer patients suffer from major depression and in the vast majority of cases their mental anguish is being overlooked or ignored, a study has found.
A survey of more than 21,000 patients in Scotland found rates of clinical depression ranging from 6% to 13%, compared with a prevalence of just 2% in the general population.
Of the 1,130 who had been diagnosed, almost three quarters (73%) 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 short-comings 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 (eg prostate and bladder) or gynaecological cancers.
All 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%) followed by patients with gynaecological cancers (10.9%) and breast cancer (9.3%).
Seven per cent of patients with bowel cancer were seriously depressed, as were 5.6% of individuals with genito-urinary cancers.
At the time of screening, 73% of 1,538 patients diagnosed with depression for whom information about treatment was available were not receiving "potentially effective" therapy for their mental state.
Author Dr Stefan Symeonides, from the University of Edinburgh, said: "Day to day in the cancer clinic oncologists like myself are aware that depression is a profound problem for patients who already have enough to deal with.
"However, this may just be the tip of the iceberg."
The new treatment approach, costing £600, involves talking to patients, helping them to be active and engaged, "problem solving therapy" aimed at putting people more in control of their situation, and intensive monitoring for up to a year.
Patients randomly recruited to the programme had their progress compared with those who continued to undergo "usual care". This generally involves GPs being in charge and prescribing antidepressants or referring patients to mental health services if necessary. It also usually means a patient has to seek help before it is given.
For 500 patients with a good cancer prognosis, 17.3% of those getting usual care saw a significant improvement in their scores of depression symptoms after six months. But 62% of those allocated the new therapy programme experienced a similar positive outcome - a difference of 45%.
As well as not feeling so depressed they were also less anxious, less fatigued, less afflicted by pain, and their quality of life was greatly enhanced. The difference in improvement was sustained for the whole of the 12 month follow-up period.
The second trial, SMaRT Oncology 3, focused over a period of 32 weeks on patients with lung cancer who had a poor prognosis. Depression severity was found to be "significantly lower" in those assigned to the new treatment compared with those undergoing "usual care".
Self-rated levels of depression improvement, anxiety and quality of life were all better for patients who continued to respond to the new treatment for 12 weeks.
SMaRT Oncology 3 leader Dr Jane Walker, from Oxford University, said: "Patients with lung cancer often have a poor prognosis. If they also have major depression that can blight the time they have left to live. This trial shows that we can effectively treat depression in patients with poor prognosis cancers like lung cancer and really improve patients' lives."
Funding for the studies came from Cancer Research UK and the Chief Scientist Office of the Scottish Government.
Jacqui Graves, head of health and social care at the charity Macmillan Cancer Support, said: "Cancer can have a devastating impact on patients, causing many to feel alone and isolated, and we know that a huge number of patients will experience depression.
"Depression may be a temporary reaction to a patient's diagnosis and something that can be addressed through information and support, but in other cases it can be more complex and a patient may need therapy or medication.
"It's heart-breaking to think that cancer patients who are already dealing with the toughest fight of their lives are also struggling with depression, without adequate support.
"Anyone experiencing depression should get in touch with their GP. Macmillan provides information and support for people affected by cancer through its telephone helpline."
The charity's Support Line can be contacted on 0808 808 0000.