ABC of clinical haematology: Chronic myeloid leukaemia

Introduction

Chronic myeloid leukaemia is a clonal malignant myeloproliferative disorder believed to originate in a single abnormal haemopoietic stem cell. The progeny of this abnormal stem cell proliferate over months or years such that, by the time the leukaemia is diagnosed, the number of leucocytes is greatly increased in the peripheral blood. Normal blood cell production is almost completely replaced by leukaemia cells, which, however, still function almost normally.

Chronic myeloid leukaemia has an annual incidence of 1 to 1.5 per 100 000 of the population in the United Kingdom (about 700 new cases each year), with no clear geographical variation.

Presentation may be at any age, but the peak incidence is at age 40-60 years, with a slight male predominance. This leukaemia is very rare in children.

Most cases of chronic myeloid leukaemia occur sporadically. The only known predisposing factor is irradiation, as shown by studies of Japanese survivors of the atomic bomb and in patients who received radiotherapy for ankylosing spondylitis.

The clinical course of chronic myeloid leukaemia can be divided into a “stable” or chronic phase and an advanced phase, the latter covering both accelerated and blastic phases. Most patients present with chronic phase disease, which lasts on average four to five years. In about two thirds of patients the chronic phase transforms gradually into an accelerated phase, characterised by a moderate increase in blast cells, increasing anaemia or thrombocytosis, or other features not compatible with chronic phase disease. After a variable number of months this accelerated phase progresses to frank acute blastic transformation. The remaining one third of patients move abruptly from chronic phase to an acute blastic phase (or blastic crisis) without an intervening phase of acceleration.

Pathogenesis

All leukaemia cells in patients with chronic myeloid leukaemia contain a specific cytogenetic marker, described originally in 1960 by …