Person_man
You know, if healing magic fixes congenital problems, but not cancer, the issue might be in intent. If it can fix congenital issues, then it's more flesh shaping than restoring to baseline. That would fall under the Alteration school rather than Restoration. Technically, once someone knows the problem they can reshape the subjects body.
I always liked the take on healing magic that too much of it can cause cancer, since it focuses on regrowth so much. It might be possible to retool spells to focus on the differences between cancerous and non cancerous cells if you know what you're doing. Erana hasn't been at this for too long, and her heals seem more of a spray and pray magic than a finely tuned instrument.