Excel 2007 : Join multiple field and ignore blank/false fields

If I have a list of cells that are based on a control form that result in a true or false outcome. And I want to list only those items that are true in a sentence. Example

Example of table

Stoke True
Cancer True
Smoker False

Example of desired outcome:

John has a medical history of: Stoke, Cancer.

I can use the concantante function, but it put's "," in between all cells even if they are false.