Prognostic impact of chromosomes 17 and 18. Absence of a gain of either chromosome 17 (left panel) or chromosome 18 (middle panel) is associated with poor prognosis in patients with HD-ALL; concurrent absence of a gain of both chromosomes 17 and 18 (right panel) is associated with very poor prognosis. Tri/tetra 18 and 17: HD-ALL with trisomy or tetrasomy 18 or 17. Others: HD-ALL without gain of chromosomes 17 and/or 18.