ABSTRACT
The 2016 World Health Organization revised classification of tumours of haematopoietic and lymphoid tissues has been widely accepted by pathologists and clinicians, thereby halting many historical and current controversies and greatly facilitating research. This chapter introduces this revised classification and discusses the impact of the principal subtypes of haematological malignancies on individual diagnosis and treatment. It also discusses some of the associated risk factors. A principal feature of leukaemia is stem-cell-derived haematopoiesis with altered proliferation and differentiation leading to an excessive accumulation of abnormal leukaemia cells in the bone marrow and peripheral blood. Monoclonal gammopathy of unknown significance, smouldering multiple myeloma, and multiple myeloma represent a spectrum of disorders with an increase in tumour burden with the eventual development of organ damage. The notion of an age-related increased risk for haematological cancer in persons who harbour clonal haematopoiesis of indeterminate potential appears reasonable, but it remains an enigma as a risk factor for many other cancers.
