A previously well teenage Caucasian boy presented to the paediatric clinic with headache and myalgia. His past medical history was otherwise unremarkable. Physical examination showed petechiae over his arms and legs. Peripheral blood smear showed moderate anaemia and severe thrombocytopenia. The cerebrospinal fluid was negative. Bone scan was normal.

Examination of the bone marrow (BM) aspirate showed a diffuse infiltrate by a population of intermediate-sized mononuclear cells that existed singly or in clusters. The tumour cells had vacuolated cytoplasm, round nuclei containing multiple …