HDAC9 and mature T-cell and NK-cell non-Hodgkin lymphoma: This review will provide an overview of PTCL, including its diagnosis and treatment; discuss the role of HDAC inhibitors as anticancer agents; describe romidepsin and its use in clinical trials for patients with relapsed/refractory PTCL; and summarize recommendations for advanced practitioners (APs) when caring for patients receiving romidepsin for PTCL.