When the body is influenced by stress it releases hormones, specifically cortisol and adrenaline.  In combination, these two hormones comprise the "fight-or-flight" response and cause an increase in blood pressure, heart rate and blood sugar levels.  

Experts believe that small doses of these stress-induced hormones can be beneficial, but when they persist for long periods of time, they can be damaging to your health.

Chronic stress can increase the risk of heart disease, obesity and depression, and can foster unhealthy behaviors including substance abuse and overeating.  A weakened immune system can leave you susceptible to many illnesses, including virus-associated cancers.

I recommend my patients focus on both improving physical and mental health.  While a causal relationship has not been established between stress and cancer, an association surely exists.