The rate of depression among cancer patients has been overestimated, a review of dozens of studies suggests.

According to the review, nearly 1 in 6 people with cancer (16.5 percent) shows symptoms of clinical depression. Past studies and the National Cancer Institute estimated the rate at 1 in 4.

The new review by Alex Mitchell, of the University of Leicester in England, and his colleagues also found that the rate of depression was no higher among people who had no hope of surviving cancer than among other cancer patients.

Even if the rate of clinical depression has been overstated, nearly a third of all cancer patients have a mood disorder of some sort, which, other than major depression, can be anxiety , dysthymia (chronic mild depression) or adjustment disorder (significant stress), Mitchell told MyHealthNewsDaily.

"Clinicians and researchers really shouldn't focus just on major depression , said Mitchell, who called it a relatively small subgroup. "It is important to also look for minor depression, anxiety disorders and adjustment disorders," he said.

Mitchell and his colleagues looked at the mental health histories of 14,078 cancer patients who had participated in any of 94 studies that took place from 1978 to 2010.

They found no difference in depression rates between cancer patients being treated to cure their disease, and those late-stage cancer patients taking medication only to relieve symptoms.

"People thought depression was very high in the late stages; some even thought it was an invariable complication," Mitchell said. "We clearly show there is no greater rate in these settings."

The rates of depression and mood disorders were not affected by cancer patients' age or gender, according to the study.

Depression can bring health complications for cancer patients, Mitchell said. It increases suffering, reduces the likelihood a patient will comply with cancer treatment, makes hospital stays longer and even affects patient survival.

And any mood disorder can increase distress, affect daily function, increase the risk of future depression and dampen the quality of life, he said.

Past research showing higher percentages of depression include a 1998 review in the European Journal of Cancer Care. It estimated 20 to 25 percent of cancer patients suffer often unrecognized and untreated long-term depression.

A 2010 study in the Medical Journal of Australia showed that 22.7 percent of 266 cancer patients were likely depressed, and 25 percent of patients had both depression and anxiety.

The new study was published Jan. 18 in the journal The Lancet.

Pass it on: Depression occurs in 1 in 6 cancer patients, but mood disorders, which can include depression, anxiety or stress, occurs in nearly 1 in 3 cancer patients.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @AmandaLChan.