Abstract
A patient with chronic myeloid leukaemia who developed widespread bone marrow necrosis associated with evolution of a new cell clone and with aggressive behaviour of the myeloid tumour in extramedullary sites is described. Cell necrosis in extramedullary tumours was also present; the sharp demarcation between zones of necrotic cells and intact cells and the histological evidence of vascular invasion by tumour cells suggest a vascular basis for cell necrosis.