What is you approach for first line treatment in an elderly patient >85 years of age with good PS and a hairy cell leukemia variant?  

The 1st question is: does he need treatment? Such as significant cytopenia(s), symptomatic splenomegaly, or constitutional symptoms? If so, and at > 85 yo, I will probably try rituximab alone after discussing with him that this is typically reserved for a relapsed disease, but the alternative is ...

If he has a good PS and he needs treatment, Pentostatin Q 2-3 weeks can be considered. Rituxan may be an option too.