Your parents may not be able to get you out of the class, but they may be able to lobby the principal to get you put with another teacher, or getting the teacher an aide or long-term sub that would give the class some coherent teaching.
Yes, a teacher dealing with breast cancer treatment deserves sympathy, but the school has the duty to make sure there is a capable instructor for your class.
Also, agree with buying some AP prep materials, checking out youtube videos, etc. If you don’t get a new teacher, you’re going to have to learn the material some other way.