bcr/abl mRNA in leukemic blasts of an unusual patient with acute lymphoblastic leukemia followed after 5-year remission by chronic myelogenous leukemia in blast crisis.

A 13-year-old boy without any previous illness was diagnosed as suffering from acute lymphoblastic leukemia (ALL). After a period of apparent complete remission until 17 years of age, the presence of Ph1 positive cells in bone marrow was demonstrated by karyotype analysis. This finding suggested chronic myelogenous leukemia (CML) because of the absence of blastic changes in bone marrow but mild leukocytosis with basophilia at that time. Six months later he had a relapse (blast crisis) with the appearance of peroxidase negative lymphoid blasts and myeloid surface markers. To make differential diagnosis, leukemia blasts at onset and relapse were examined for rearrangement of immunoglobulin JH gene and bcr/abl fusion mRNA, and were found to have the same JH gene rearrangement pattern and the same bcr/abl mRNA of bcr exon 2/abl exon 2. These results indicate an unusual case of CML which appeared in blast crisis at onset, followed by a long-term remission.