Three examples are presented to illustrate the importance of retroviruses and associated oncogenes in neoplasms of the immune system. In adult T-cell leukemia/lymphoma the HTLV I-provirus is often integrated in the human genome on chromosome 8 adjacent to the c-myc protooncogene. Cytogenetic studies of Burkitt's lymphoma (translocation of a chromosome 8 fragment) and a case of mycosis fungoides (trisomy of chromosome 8) indicate that the same oncogene may possibly be activated not only by retroviruses, but also by chromosomal aberrations.
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