Purpose of needle biopsy for existing lung cancer

My step-father has terminal lung cancer with heart disease.  He's had this for about two years.  (He was not expected to live but a few months) They cannot do surgery on him because of his heart disease.  However, he did have a round of radiation. It did shrink the tumor down enough that he did not have as much pain on his side.  He still does have some pain though. He recently had a PET scan and nothing has changed.  His physician now wants to do a needle biopsy.  What is the purpose of this?  Will it show if it is active or non-active?  Would it do any good to know since they probably won't do anything? Or could they possibly do something? (praying they can) His concern is that he doesn't want to go through all the pain (and possible lung collapse) again if they can't help him. You quick reply would be greatly appreciated since he has to let the doctor know soon.
Thank you.
Praying for my pop-pop.

[Connie 1]

how's your pop-pop?  what'd he decide?  the needle biopsy helps figure out stuff about the tumor.  did he have it?  did it help?

[HeinrikMD]

Hi,
Your concerns are very valid. If it will not change the decision, then it may not make a difference.
There are some new drugs with side-effect profiles very different from conventional agents. If your pop is going to receive some of these drugs - then there may be some tests that would require specimens of the tumor. IF this is available, then he may have a new option for treatment.
Best to discuss your concerns with your doctor.