British researchers have found that one-quarter of patients with advanced cancer have depression that had previously not been diagnosed.

The effects of depression can be as difficult to cope with as the physical symptoms of a terminal illness such as cancer, said lead researcher Mari Lloyd-Williams of the University of Liverpool.

Patients often feel useless, that they are to blame, and even experience suicidal thoughts during cancer - these are all signs of depression but rarely elicited.During advanced cancer, when the disease has begun to spread from its original tumor, depression is difficult to diagnose as symptoms can be confused with a patient displaying appropriate sadness - feelings that commonly result from suffering a terminal illness.

The researchers developed a tool to detect depression in cancer patients using a screening system originally developed for sufferers of post-natal depression. The tool - known as the Brief Edinburgh Depression Scale - includes a six-step scale that assesses a cancer patient's mental condition. The test includes questions on worthlessness, guilt and suicidal thoughts.

The research has been published in the Journal of Affective Disorders.