It is not possible to prevent tumors that start in the brain. Metastatic tumors can sometimes be prevented by making good lifestyle choices. For example, a person can quit smoking to lower the risk of lung cancer.
Long-term effects depend on the type of brain tumor. If left untreated, noncancerous brain tumors may grow so large that they put pressure on the brain, leading to death.
Brain tumors are not contagious. They pose no risk to others.