The molecular biology of acute myeloid leukemia. Proto-oncogene expression and function in normal and neoplastic myeloid cells. Proto-oncogenes and suppressor genes fall into four functional groups: growth factors, growth factor and hormone receptors, signal transducers, and transcriptional regulatory factors. Many of these genes are selectively expressed in myeloid cells and may play a role in normal development of the myeloid lineages. Furthermore, chromosomal rearrangements, deletions, and mutations may disrupt the normal expression or function of these genes, promoting MPD and leukemogenesis. Many of the genes altered by karyotypic abnormalities in myeloid disorders are only beginning to be identified. Future studies undoubtedly will determine the molecular mechanisms whereby these genes, residing at karyotypic breakpoints in myeloid disorders, promote neoplastic transformation of myeloid cells. 