Try to put it behind you as worry won't help (easier said that done, right?). Looks like you're doing something called ruminating, and a field of psychology called CBT (cognitive behavioral therapy) has a way of dealing with this through their ABC(DE) model.
Im not a psychologist, nor do i have a great grasp of the therapy, so of i get this wrong forgive me, just trying to help the bet way i can.
The way the above works, is that you're making your thoughts your reality, and that's making you miserable. Change your thoughts, change your reality. The A is the action, you got cancer. The C is the consequence, you're experiencing anxiety. The ABC model states that is NOT the cancer that is causing this anxiety, but the beliefs (the B part) you have about the cancer. So change the belief and change he outcome,