But the latest findings suggest that the link between the symptoms and depression remains strong even after physical causes are accounted for, according to Dr. Yosuke Uchi-tomi of the National Cancer Center Research Institute East in Kashiwa, Japan.
"Other symptoms, such as sleep disorders and fatigue, may not be as useful for the diagnosis of major depression in cancer patients," Uchitomi said.
"Major depression is among the most widely recognized psychiatric disorders in cancer patients. It not only produces serious suffering, but also worsens quality of life, reduces compliance with anti-cancer treatment, can lead to suicide, and is a psychological burden on the patient's family."
Uchitomi and his researchers asked 220 cancer patients with depression if they suffered from symptoms like loss of appetite, weight loss, insomnia and oversleeping, and diminished ability to concentrate.
Patients who reported weight-loss and appetite-changes, or an inability to concentrate, were significantly more likely to also report a general lack of interest and pleasure, called anhedonia, that is characteristic of depression.
Patients who had lost weight or their appetite had more severe depression than those without these particular symptoms.
The findings suggest that some physical symptoms in cancer patients may be more valuable for diagnosing depression than previously thought, and should be considered separately rather than in combination with other factors, Uchitomi said.