Cytogenetic and molecular evidence of marrow involvement in extramedullaryacute myeloid leukaemia

A diagnosis of granulocytic sarcoma was made in a a-year-old child based on the detection of myelomonocytic blasts in tissue obtained from a subcutane ous nodule with no evidence of concomitant disease in the bone marrow. The child responded to systemic chemotherapy and is in remission 3 years later. An identical clone with an in frame fusion of the MLL and AF10 genes was i dentified from both tissue and bone marrow samples. The generation of an in frame MLL-AF10 fusion requires complex intra- and interchromosomal exchang es between chromosomes 10 and 11. In this case, an intrachromosomal rearran gement of chromosome 5 was also observed. This case illustrates the presenc e of systemic disease in extramedullary leukaemia, its response to systemic rather than topical therapy and suggests that the events leading to chromo somal translocations in leukaemia may be part of a generalized intracellula r event.