Percentage of cell recovery after 7 days of culture on stroma among different subgroups of hyperdiploid 51-to-65 ALL, including cases without and with duplications of chromosomes 4 and 10, ≤ or >55 chromosomes, and without and with structural chromosomal abnormalities. Numbers of leukemic lymphoblasts before and after culture were counted by flow cytometry as described in Materials and Methods. Horizontal bars indicate the median cell recovery in each group.