It is widely accepted that psychological stress and mental illness can compromise the function of the immune system. Clinical and epidemiological studies on humans recognized that specific psychosocial factors, such as stress, chronic depression and lack of social support are risk factors for the development and progression of cancer. Unfortunately, most of the animals studies on this subject are based on laboratory tests performed on mice. This retrospective cohort study aims to analyze the relation between stress and tumor in pet dogs, by evaluating and comparing the stress level in two groups of 69 dogs each, balanced for sex and age: the oncologic group consists of dogs diagnosed with cancer and the control group consists of healthy dogs. Our results show that, before the cancer diagnosis, more dogs in the oncologic group faced changes in their household and routine as opposed to the control group (p<0.05). More dogs of the oncologic group than the control group also showed signs of stress and anxiety, before the cancer diagnosis (p<0.05). As reported by their owners, these included attention seeking, hiding without a specific reason, following the owner around the house, hyper-vigilance, fear of fireworks and gunshots, biting, aggression towards other dogs, licking and chewing excessively parts of their body. Our results are aligned with the evidence from human research, indicating that dogs with cancer are significantly more likely to have shown signs of stress compared to the control dogs during their life.
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