Do shadows on the lung often turn out to be cancer? any help appreciated!!!!

All of this has happened to me within the last week! The Dr sent me for blood tests and a chest xray - as a matter of urgency (according to my Dr) i have been referred to a specialist. The xray revealed a 'shadow' on my left lung. I know that a simple xray is not 100% diagnostic but i cant stop thinking about outcomes, from it not being cancer to having weeks to live! I cant begin to deal with this until i know what is what. It's this damn waiting!!!! Even a diagnosis of cancer would break this waiting and wondering - I feel i am in some type of limbo. It's the uncertainty Do these shadows often turn out to be cancer? Ive had a cough for months, get night sweats and i feel so old at 40 - tired and fatgued. Ive smoked for ten years, stupidly x