Figure 2.

Clonal relationship of diagnosis and relapse samples in ALL. The majority of relapse cases have a clear relationship to the presenting diagnosis leukemic clone, either arising through the acquisition of additional genetic lesions, or more commonly, arising from a ancestral (pre-diagnosis) clone. In the latter scenario, the relapse clone retains some but not all of the lesions found in the diagnostic sample, while acquiring new lesions. Lesion specific backtracking studies revealed that in most cases the relapse clone exists as a minor sub-clone within the diagnostic sample prior to the initiation of therapy. In only a minority of ALL cases does the relapse clone represent the emergence of a genetically distinct and thus unrelated second leukemia.