Frequency and importance of change in blast cell karyotype in relapsing childhood lymphoblastic leukemia.

Blast cell chromosome abnormalities at presentation in childhood acute lymphoblastic leukemia (ALL) are common, and different patterns are known to be related to outcome. In contrast, the frequency and importance of further changes at the time of relapse remain unclear. Blast cell karyotype evolution was therefore studied in a group of children with recurrent disease. Of 134 consecutive children diagnosed between 1982 and 1992, 31 had a marrow relapse, and 24 had complete cytogenetic studies at both diagnosis and the time of recurrence. Fourteen (58%) of the 24 showed additional chromosomal abnormalities at relapse, 5 (21%) retained abnormalities identical to those seen at diagnosis, and 5 (21%) remained cytogenetically normal. The 14 with additional changes had shorter first remissions and showed shorter survival after relapse compared with the others. These findings indicate that emergency of cytogenetically recognizable subclones during the progression of childhood ALL could be a marker of more resistant disease.