Comparative Southern blot analysis of

IGH gene configuration in 6 precursor-B–ALL patients. Monoclonal patients 5438 and 5260 (patient with trisomy 14) show identical gene rearrangements at diagnosis and at relapse. In monoclonal patient 5117, one allele at relapse is deleted and another one is preserved. Patient 5257 demonstrates biallelic IGHdeletion at both disease stages. Oligoclonal patient 4910 and monoclonal patient 5282 (the upper weak band in the diagnosis lane is derived from previous hybridization) show completely changedIGH gene rearrangement patterns. While sequence analysis has proven a clonal relationship between diagnosis and relapse in patient 4910, patient 5282 most likely represents a secondary ALL.