First of all, so sorry for you to have to deal with 2 problems! However; when you go to the doc....load up with the same kind of questions you ask here.
Ask what is the best treatment for each disease and will any one treatment actually benefit the other disease? Will one treatment hinder the other? Make the doc explain what each med is doing to your body and how do they relate to each other.

My mom had scleroderma and cervical cancer. She had a total hystorectomy but given no replacement hormones because that type of cancer does not react well to hormones.
However; hormones help scleroderma so her scleroderma went wild. They opted to begin hormone treatment again earlier than planned due to the racing scleroderma problems.
You just don't know how things intermingle and its soooo important to learn as much as you can so you can ask the really big questions. Make them explain EVERYTHING to you so you can walk away feeling satisfied with the answers and your course of treatment.
Again, I am so sorry you have to face these things.....