Stress
A study [6] conducted to assess the effects of stress in triggering cells to become cancerous, does not give a good news related to tumorigenesis. Physical and/or emotional stress can induce signaling pathways that can then initiate cellular proliferation to the point of becoming abnormal.
Oxidative stress is also another form of cellular suffering in response to the free radicals released during high brain activity. It can also give a lead to tumor development.