I have had a hard immovable lump behind my ear for 4 years. i am worried it is an encapsulated cancerous tumor. will an encapsulated tumor grow?

Cancer unlikely: If a mass has been there for 4 years and has not grown, it is not cancer. Should the lump double in size, ulcerate, bleed or become painful, see a doctor. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, low fat milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex.

You should: have it checked out by your doctor. You don't mention whether it feels like it is growing or not, or how big it is. If it has been truly stable over 4 years, it is extremely unlikely to be cancerous. However, it is possible for some low grade cancers to grow very slowly and almost imperceptibly over the course of years, so if it bothers you, get it checked.