Structural and functional chimerism results from chromosomal translocation in lymphoid tumors.

Publisher Summary This chapter discusses the mechanism of translocations in lymphoid tumors with particular reference to the timing of translocations in T cell tumorigenesis. The chapter discusses the consequences of chromosomal abnormalities: first, the consequences to the protooncogene near the site of the abnormality, and second, the consequences to the cell of an “activated” oncogene. The chapter presents the major lymphoid abnormalities that have been cloned so far together with relevant information about the location of the presumptive oncogenes involved. The oncogenes affected by the abnormalities range from previously known oncogenes to newly discovered ones. The mechanism by which chromosome abnormalities associated with the rearranging genes are created has been discussed. The enzymes carrying out normal antigen–receptor gene rearrangement are implicated in the creation of these abnormalities. The chapter describes gene fusion resulting from chromosome translocation. Fusion of two transcription units was first described in cancer associated chromosomal abnormalities in chronic myelogenous leukemia, wherein it was discovered that the c- abl protooncogene was consistently joined to another gene in the Philadelphia chromosome translocation. The study of chromosomal abnormalities in human T cell leukemias has illuminated some of the features of tumor progression. The study of translocations and inversions in Tcell tumors from patients with ataxia telangiectasia (AT) has provided some important insights into the conversion of preleukemia to overt leukemia.