Israel Institute of Technology researchers stated that Positive thinking could help fight cancer and boost survival rates.

The scientists explored the possibility of the brain’s reward system fighting the tumor in mice. Some immune cell subset like Myeloid-Derived Suppressor Cells (MDSCs) favors the growth of cancer. They artificially stimulated the reward system in the brain of mice by boosting the levels of dopamine, a neurotransmitter which regulates pleasurable feelings. Reduction in the activity of MDSC was seen.
50 Percent Reduction in the size of the tumors was observed after 14 days of continuous treatment.
The impact of positive thinking is unknown because most of the earlier studies focused on the negative emotions like stress and depression.
Source-Medindia