Given the task definition and input, reply with output. Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Context: In patients with active rheumatoid arthritis despite therapy with DMARDS, treatment with a spleen tyrosine kinase inhibitor has achieved similar response rates to those achieved in clinical trials of other drugs, including biologic agents. Where might these agents fit in the current armamentarium against this disease?
Question: Which enzyme is inhibited by a drug fostamatinib?
spleen tyrosine kinase