Information on the presence of specific chromosomal structural abnormalities in certain tumors has been increasing. Although the tumor specific chromosomal abnormalities were deemed important, it was not until the chromosomal location of several oncogenes was determined that the real molecular significance became apparent. It now appears that many of the genes associated with animal tumors are located near specific translocations in human cancers. The specificity of chromosomal changes have not only been used diagnostically and prognostically, but also they present key information for the molecular analysis in determining the nature of the genes of human neoplasia. In recent years, great advances have been made in our understanding of the molecular structure of the specific chromosomal translocations in certain hematologic disorders. The present report will briefly describe chromosomal rearrangements and how oncogenes or cancer related genes involved can be affected.