Welcome to Grace. It’s true a CT especially a hi res CT would pick up a pancoast tumor. You’re probably looking for something less complicated. I have to admit we get a lot of people who have shoulder pain that radiates down the arm who are worried they have a pancoast tumor. I hope you also find that there are other much more common and probable reasons why this is happening. The odds are extremely small that a 28 year old with a small smoking history has lung cancer add to that the rarity of a pancoast tumor especially without a significant smoking history. A nerve that is pinched or damaged is tons more common than a pancoast tumor in a 50 year old with a smoking history. I hope you get this resolved hopefully through physical therapy.