When Mom was in the nursing home we were caring for her Boston Terrier who was diagnosed with Cushings. This was 7 years ago so my memory on the facts are not 100%.
She was treated with Lysodren, if I remember right was a form of a chemo treatment. Her minor issue was the urinary infections, she suffered horribly with skin issues.
My brother and I struggled with the decision on how far to take the treatments but just couldn't give up since Mom was confident that both she and the dog would get better and go home. I finally made the decision to put her down as the treatments just didn't work. While she seemed happy and in no pain, she ended up looking like a zombie dog from the very bad skin issue. We lost Mom later that year as well. Sorry for the downer post.