I agree that you should fight this decision. A "biosimilar" is really a different drug. It's not a generic form of the same drug. For that reason, many insurers, mine included, are not requiring patients currently on a biologic to switch once a biosimilar becomes available. They are instead requiring that patients who have never been on a biologic to try a biosimilar, if available, before starting the biologic it mimics. You have a good appeal.