No, he has no legal right to know your medical history or present information.  You are protected under medical privacy laws at the federal level, and while he does have a legal right to obtain up to date and complete medical information about his child, that does not include you and your current diagnosis.

While most medical facilities know that they cannot provide information to an ex-spouse, it may be a good idea for you to add a note to your medical records files at your regular doctor and hospital that no one is to receive information without your permission.

I wish you a happy and cancer free future.