need opinions on CT results

My husband had a CT scan in the hospital were he was admitted for a bowel obstruction and we were told to have a PET scan after he was released due to an incidental finding in his lung that showed on the scan.  My husband "doesn't want to know" and won't follow up.  The finding was  4.4 cm x 2.1cm x 3.3 cm peripheral mass at the left lung base.  differntial includes round atelectasis versus neoplasm.  small right effusion, right basilar atelectasis.

My research leads me to understand that a pleural based mass is usually a met not a primary tumor.  His abomen was scanned too and there was mild thickening of the walls and inflammatory changes in the presacral area.  Liver and other organs were not mentioned as worrisome.  Where could a primary be hiding?

He is 86 and had rectal cancer 30 years ago.  

If this pleural based mass in cancer, won't it lead to effusion eventually?  I can accept his decision not to get treatment at his age, but I would sure like to know what we are dealing with.  I would appreciate any opinions, input or suggestions.  Thank you so much.