your father must be going through terrible physical and emotional pain.
Have faith in God and pray ceaselessly.
Also ask him to practise auto-suggestions. They are positive sentences said to oneself repeteadly. And they work, believe me, its my exprerience.
I wil give u the name of a site which has the section healing cards in it. U have a positive affirmation card for each disease. Ask ur father to see that or u c that and say the affirmation that is applicable.
It wil work but it has to be done wd faith. Ur father should say it with complete belief in the affirmation and in God.
The name of the site is www.vitalaffirmations.com
Also he should keep saying to himself- "I am cured of lung cancer". Keep praying to God, He wil heal ur father.