Preleukemias.

A chromosomally abnormal clone is demonstrable in the bone marrow of a significant number of patients with hemic disorders that carry an increased risk for the subsequent development of leukemia. These "preleukemia" states include a variety of cytopenias, myeloproliferative disorders, and childhood syndromes. The cytogenetic alterations that occur nonrandomly in these dyscrasias are often similar to those observed in acute nonlymphocytic leukemia and in the accelerated phase of chronic granulocytic leukemia: monosomy for chromosome 7; trisomy for 8,9,21, and the long arm of 1(1q); deletions of 5 and 20 (5q-, 20q-); and an isochromosome derived from 17 (iso 17q). These findings support the view that despite clinical differences, these various preleukemic disorders are all characterized by the presence in the hematopoietic tissues of a clone of cells derived from an altered hemic stem cell. Furthermore, the data suggest that preleukemia, chronic leukemia, and acute leukemia may be fundamentally similar diseases, differing primarily in the rate at which the aberrant clone is expanding. Chromosome studies may be of prognostic value in the cytopenic preleukemias. Patients with abnormalities show a decreased survival and are at increased risk for progression to acute nonlymphocytic leukemia. In the myeloproliferative disorders and the preleukemic childhood disorders, cytogenetic alterations are not clearly predictive, and aberrant clones may persist for years without clinical progression.