Cancer Linked to Clinical Depression in Rats
I always am saddened when I diagnose cancer in a patient. However, the remorse I feel when making the diagnosis generally has been tempered by a small silver lining. Most of the cancer patients I treat do not seem to realize that they are sick. Although humans with cancer often suffer profound psychological effects from the diagnosis, most pets behave as if they feel fine until the disease causes serious complications.
Or so I had thought.
A brief article in the June 5, 2009 issue of The Week has given me a reason to look harder at the quality of life of my cancer patients. It also has given me another reason to hate cancer--as if I needed one.
Tumors are doubly depressing
A diagnosis of cancer is obviously a good reason to be depressed. But new research finds that the feeling isn't just psychological: Tumors produce high levels of a chemical that can effect [sic] mood and make people feel down. Behavioral neuroscientists at the University of Chicago compared depression and anxiety rates in groups of rats with and without tumors. Since rats have no awareness that they have cancer, Dr. Brian Pendergast tells BBCnews.com, "their behavioral changes were likely the result of purely biological factors." He found that rats with cancer exhibited signs of depression and anxiety, floating passively when placed in water while cancer-free rats swam for safety. The tumor-ridden rats also hoarded and buried objects they were given, and lost interest in eating sweets. The scientists believe that the anxious and depressive behavior is connected to levels of chemicals called cytokines, which are produced by tumors and also by the immune system when it's battling cancer. Rats with tumors had double the normal level of cytokines, which have a direct, depressing effect on emotional centers in the brain.
Note that this study does not say anything specifically about dogs or cats. But it does give me an additional reason to hope that some major breakthroughs in cancer research will come soon. For the record, I think they will.
Also, be aware that a great deal of research currently is directed towards understanding and modifying cytokines (cytokines are linked to pain and a number of other physiological responses that might be modifiable through pharmaceuticals). However, in the case of cancer, there is no doubt that the best approach is not to target cytokines. The best tactic is to cure the disease.