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It is important to complete the treatment as Doctor advises. His prognosis will also depend on the spread of the tumor
and grade of the tumor. Let him have protein rich diet like cereals pulses, eggs, chicken, lean meat, soyabean in his diet in which ever form he is taking diet. He needs to be well hydrated. Give him all support. Since he is receiving chemoradiation his life will be prolonged to some extent though it is slightly more aggressive tumor. Leave the rest in hands of God as he is getting best care from his Doctors.