Are there official recommendations for treating leukemia?

Yes. Check nccn. Org, they have guidlines for multiple cancer types including all types of leukemia.
Official is an. .... Interesting word. Perhaps more accurately, there are standards of care for primary therapy for virtually all types of leukemia. Oncologists strive to follow these norms when they can, because they have been established by an iterative process of improvement (the clinical trial). For relapse disease, there is more "professional license" invoked. Much information can be found on the nci website.