Social isolation may make cancer more deadly, US researchers say.
Researchers studied female mice genetically predisposed to mammary gland cancer, which were stressed because they were separated from their mothers.
They found they developed more and larger mammary gland tumours compared to more contented animals.
This suggests social environment can modify the biology of the disease, said the journal Cancer Prevention Research.
The researchers said more work was needed to pinpoint which cell types were affected.
Previous research has found social isolation has been linked to an increased risk of death from several chronic diseases, while depression can have a negative effect on cancer prognosis.