Figure 1. Model of evolution of relapsed disease.
A preleukemic stem cell (LSC, light blue) gives rise to frank ALL (dark blue cells). Intrinsically drug resistant clones (red) may be present at diagnosis at low levels. However, LSCs and other subclones may survive initial treatment and acquire additional lesions that result in acquired drug resistance. Rarely, relapse clone is genetically distinct from that at diagnosis (second malignancy).