Langerhans cell histiocytosis and myelomonocytic leukemia: a non fortuitous association.

Background. Langerhans cell histiocytosis is an uncommon clonal disorder. i ts reactional or genetic nature is debated. Case report. Three patients aged 71, 75 and 71 years with Langerhans cell h istiocytosis also developed myelomoncytic leukemia (AML(4), AML(5), and chr onic myelomonocytic leukemia). In two cases, there was no prior treatment w hich could potentially induce leukemia. In the third case, AML4 occurred sh ortly (10 months) after initiation of a vinblastin treatment. Discussion. This pathogenic association suggests a common origin for these two conditions, corresponding to an anomalous pluripotent stem cell line. T hese cases provide further evidence favoring the hypothesis of a genetic or igin rather than a reactional origin for Langerhans cell histiocytosis.