Animal models for tumor progression (short review).

During recent years the number of studies concerning tumor progression has increased considerably, with the important breakthrough in the study of neoplastic development being the selection of variants of malignancy. Some of the models used for the selection of these variants and the assays for malignancy by which they are tested are, however, quite remote from the natural process of tumor progression. Various models are herein discussed with their advantages and drawbacks evaluated. The validity of the models for the testing of antitumoral drugs at various stages of tumor progression are also discussed.