Arm And Shoulder Pain

I have had arm and shoulder pain for few months now. I thought I may have injured my shoulder at work. I have been to physician to have mri to see if the rotator cuff is torn or something. Mri said it is not torn. Physician suggested I come back for some type of scan to see if there may be tumor in the area top of my lungs. Said this may cause pain to go to my shoulder. I have never heard of this. Why did he suggest this? Doctors office is to call me soon to schedule the scan. What could he be looking for. How could my shoulder pain be related to a tumor in the upper lung area?