Biology of the lymphomas: cytogenetics, molecular biology, and virology

Correlations between cytogenetics, histology, and clinical course continue to emerge in studies of non-Hodgkin's lymphomas. The previously recognized association between the t(14;18) chromosomal translocation and follicular lymphoma has been confirmed; abnormalities of chromosome 3 have correlated specifically with diffuse large cell lymphoma and abnormalities of chromosome 1 have been frequently present in T-cell lymphomas. Rearrangements involving 11q13 (bcl-1) occur most commonly in diffuse lymphocytic lymphoma of intermediate differentiation. Several new recurrent chromosomal abnormalities have also been described. The molecular fine structure of the t(8-14) chromosomal translocation in Burkitt's lymphoma appears to differ between endemic (Epstein-Barr virus-associated) and sporadic cases. In endemic Burkitt's lymphomas, the chromosomal breakpoint is usually far upstream of c-myc oncogene, leaving the regulatory region of the gene intact. In sporadic tumors, a large part of the regulatory region is separated from the gene and transcription is initiated at sites within the first intron. These data raise the possibility that Epstein-Barr virus may contribute to the deregulation of the c-myc gene and that this interaction may be required for tumorigenesis in the presence of some, but not all, types of c-myc damage arising from chromosomal translocations. Partner proteins that oligomerize with c-Myc have been identified in humans and mice (Max and Myn). The partners share with c-Myc the DNA-binding and coiled-coil motifs that are recognized in many other proteins and that function as transcriptional regulators. The Bcl-2 protein has been shown to be a mitochondrial inner membrane protein that blocks programmed cell death (apoptosis). Viral expression has been demonstrated in Epstein-Barr virus-associated Hodgkin's disease, and the spectrum of Epstein-Barr virus-associated lymphoproliferative disease has been expanded to include some T-cell malignancies. A new human herpesvirus has been associated with some cases of Hodgkin's disease.