The role of viral transformation and cytogenetic changes in viral oncogenesis.

A wide variety of DNA viruses and a more restricted family of RNA viruses can transform normal cells in vitro. Transformation means either immortalization and/or the appearance of certain phenotypic changes. Although it has been often inferred that in vitro transformation can be essentially equated with malignant transformation, increasing evidence indicates that the latter, reflected by tumorigenicity in vivo, requires additional cytogenetic changes. The evidence will be reviewed for EB virus-associated human malignancy (Burkitt's lymphoma) and the role of the 14q + translocation marker in human B-cell neoplasia. These findings point to an initiating role of viral transformation, reflected by in vitro immortalization, followed by a cytogenetic evolution where chromosome 14-associated changes are essential for the liberation of B lymphocytes from super-imposed controls. The contrast of tissue-associated, specific chromosomal changes that bring about malignant transformation after the initiating impact of different agents will be illustrated experimentally for murine T-cell lymphoma. Here, X-ray, DMBA and different virus (RadLV, Gross virus)-induced T lymphomas show the same chromosomal change: trisomy 15. It may be questioned whether viral transformation can ever lead to neoplasia in the absence of subsequent cytogenetic changes.