PET scan or Bronchoscopy/Biopsy

I was diagnosed with MAC by bronchoscopy in early May this year. Im 81 years old and had breast cancer in 2022..no evidence of disease on mammos since then. I was sent to an infectious disease dr and she sad I was her 3rd MAC patient that day and the first new patient. Anyway, because of me not having ANY of the symptoms, and my age, she said wait and watch and if I start with symptoms like lots of coughing, bed-soaking night sweats, etc I should come back immediately. I see my oncologist who follows my breast cancer treatment every 3 months. My oncologist wanted a pet scan, insurance wouldn't approve (this was before MAC diagnosis) so she got a CT of my chest and it showed the tree in bud appearance. That's when she sent me to pulmonologist for bronchoscopy which found no malignancy.but grew out MAC. He could not see the one hilar node seen on CT during bronchoscopy so on October 15 I had another bronchoscopy and he was able to get 3 samples of the node which came back as "no malignancy seen". Sorry for this being so long just wanted to give as much info as possible. The pulmonologist told me before the second bronchoscopy that he has had a good many patients with MAC "light up on a PET scan and it not be cancer.

@bbeers I don't have any expertise on this subject but I was told when my initial CT report suspected my nodules were MAC related that a PET scan cannot distinguished between cancer and inflammation, both will show as "hot" (as noted by @lulu1944). If that is true (and you will need to run that by your doctor to confirm) it seems a PET scan in your circumstances won't be very helpful as we already know you have MAC. You don't explain why your doctor thinks the new "spot" is cancer related rather than advancing MAC disease (which would seem like the more obvious first thought to me, a non-doctor), I assume it is the quality of the "spot" that raises concern for your doctor. Myself, I would want an explanation as to why the "spot" is suspected as cancer versus advancing MAC, especially as your doctor initially put you on an antibiotic (a single short term antibiotic is insufficient to treat MAC, I assume your doctor was treating a possible something else, though it doesn't sound like that was matched to a sputum sample; not clear why they are not treating your MAC). Obviously cancer is a serious consideration and not one you want to delay in diagnosing and treating. Good luck.

My pulmonologist said he "suspected" it was the MAC disease but that he has seen it look like cancer on PET scan but turned out to be the MAC disease. In my case, so far, no cancer...Thank God!

Get a bronchoscopy. That will determine if it’s really MAC and then if it is, you can start an antibiotic regimen.

@bbeers I have a couple of questions -
Have they ever done a sputum culture to determine which infection you might have? If you produce sputum with a cough, you could be able to "skip" the bronchoscopy and get the answers without an invasive procedure. (In either case, it will take 1-2 weeks to see if it is pseudomonas, 4-8 weeks to diagnose NTM/MAC.)
Then, if the results are negative, it would be time for a PET scan, though I believe rapidly appearing new spots are more usually an infection.
I might answer differently if you have a history of smoking or other lung cancer risks such as industrial exposure to chemicals or asbestos - then an early PET scan makes sense.