Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare cancer of the bone marrow. It was previously known as natural killer (NK) cell leukaemia. This booklet explains what it is, and describes the causes, who it affects, what symptoms to expect, how it is diagnosed, and treatment options. It also covers everyday life, managing your emotions, how to talk to your doctor and family and friends, survivorship, palliative care, and end-of-life care. Includes a glossary and details of further support.