It isn\u2019t out of the realm of understanding to hear that a person fighting cancer would have some mental reaction to their condition, such as depression. Depending upon the individual\u2019s prognosis, a teetering between life and death can greatly impact the person\u2019s outlook on life. Now it seems that depression associated with cancer patients is being generated by the cancer itself. The Times of India reported on findings produced by researchers at the University of Chicago. The research team determined that tumors produce chemicals, which can then produce negative mood swings. "Our research shows that two types of tumor-induced molecules, one secreted by the immune system and another by the stress axis, may be responsible," said Leah Pyter, in the Times. Pyter is a postdoctoral fellow and lead author of a paper. "Both of these substances have been implicated in depression, but neither has been examined over time frames and magnitudes that are characteristic of chronic diseases such as cancer," she added. Researchers conducted a series of tests on roughly 100 rats, some of which had cancer, to determine behavioral responses in tests of emotional state. In conducting tests that are generally used in gauging the impact of anti-depressants on rats, researchers determined that rats with tumors became less motivated to escape when submitted to a swimming test. This condition resembles that of depression in humans. In addition, rats with tumors were less eager to drink sugar water and had increased levels of cytokines in their blood and in the hippocampus, the portion of the brain that regulates emotion. The immune system produces cytokines and an increase has been linked to depression.