I hope your dad gets pain meds while he waits for treatment.
Last Feburary, I had a PET scan that showed uptake to my chest wall, left hilum and remaining lobe in my left lung. The oncologist said my cancer had come back and I should start chemo, although I could wait a while, a few months. There was not any discussion of getting a biopsy before treatment. I decided to go see a surgeon and he did a biopsy. The pathologist determined that my chest wall was clear, and so was my hilum. The nodule was malignant. So, they removed the rest of my left lung. I am cancer free now. If I had not gone to see the surgeon and had a biopsy, I would likely still have cancer. So, I guess having a biopsy would be a final conclusive proof of cancer or no cancer. My operation took place within 2 weeks after the PET scan report was completed. I am glad I had the biopsy. You might push for the biopsy to take place as fast as possible. Maybe it is not cancer. The important thing for now, is to get your dad's pain under control.
Don M