Monosomy 20 in childhood acute lymphoblastic leukemia.

We report two cases of acute lymphoblastic leukemia (ALL) with loss of chromosome 20 as the only karyotypic abnormality detected in the blast cells. The first patient is a 12-year-old boy studied at diagnosis. He represents the only case of monosomy 20 in our series of 90 pediatric ALL successfully karyotyped at diagnosis. In the second patient, monosomy 20 was detected at the second hematologic relapse, 12 years after the initial diagnosis; cytogenetic studies were not performed at disease onset.