Cytogenetically distinct leukemic cell lines displaying in vitro specific proliferative and differentiation capacities may account for early disease relapse in the blast phase of CML.

The cytogenetic features and the proliferative and differentiation capabilities of blast cell fractions purified on a density gradient were studied in one patient with chronic myeloid leukemia (CML) in blast crisis, both at the emergence and at relapse of the disease. The results show that relapse was due to the appearance of a new leukemic cell line that was characterized by peculiar chromosomal, growth, and differentiation features, which seemingly accounted for early refractoriness to therapy and disease progression.