xray?

Hi,  my dad was diagnosed with mesothelioma in Jan 2009, he has had 6 chemos, no radiotherapy or surg. as its inoperable. Drs were pleased with results from chemo and the lining was almost back to normal, he is feeling well in himself apart from constant back pain. Three weeks ago at his three monthly check up spomething showed up on the chest xray that puzzled the oncologist, thorassic surgeon and radiographer, they did not seem to think it was tumorous or suspicious  and sent him for a C.T scan. His next three monthly check up has been brought foward to tomorrow a week after the scan. Any ideas what it could be on the xray?
Thanks
K