How long have you been on Gleevec? You did not say much in your post. Were you on Sprycel at all? There is a large amount of people who have had pleural effusions due to the use of Sprycel for their CML.
If your on Gleevec, then you are mostly under the care of an oncologist. Did you ask your doctor? Your question is a bit evasive. I would speak to whatever doctor is treating you.
I'm sorry, but since I'm not a doctor, I'm not sure how to answer this.
You may be better served asking this in the Respiratory Disorderers Community:
http://www.medhelp.org/forums/show/61 or the expert forum at:
http://www.medhelp.org/forums/show/303