Spontaneous evolution of essential thrombocythaemia into acute megakaryoblastic leukaemia with trisomy 8, trisomy 21 and cutaneous involvement.

Spontaneous transformation of essential thrombocythaemia (ET) into acute leukaemia is rare. We describe a case of ET that spontaneously transformed after 19 yrs uneventful follow-up into acute megakaryoblastic leukaemia. Cytogenetic analysis of bone marrow nucleated cells showed trisomy 8 and trisomy 21 at time of leukaemic transformation supporting the hypothesis that chromosomal abnormalities are part of the mechanism that drives the leukaemic progression independently of drug cytotoxicity. In addition, the very rare and intriguing finding of M7 FAB subtype evolution of ET was complicated by cutaneous involvement in the leukaemic process.