Comparative chromosome analysis of primary and metastatic Rous sarcomas in rats

The cellular basis of tumor progression

Variability in disease presentation and course is a hallmark of cancer. Variability is seen among similarly diagnosed cancers in different patients or animal hosts and in the same cancer at different periods of time. This latter type of variability, termed "tumor progression," was defined by Foulds in a series of six rules that describe the independent behavior of individual cancers and the independent evolution of different cancer characteristics. Tumor progression is believed to result from variability among subpopulations of tumor cells within individual cancers and from selection of these subpopulations by conditions within the cancer environment, such that different subpopulations come to prominence over the course of cancer development and growth. Interactions among subpopulations, however, modulate tumor behavior as well as tumor evolution. The leading hypothesis for the origin of tumor subpopulations is the genetic instability of cancer cells. There are a number of possible mechanisms of genetic instability, some internal to cancer cells (mutation, amplification, mutator phenotypes, DNA repair deficiencies) and some present in the tumor microenvironment (endogenous mutagens). There are also potential epigenetic mechanisms of variability, including alterations in gene regulation, differentiation, adaptation, and cell fusion. Regardless of mechanism, the heterogeneity of tumor subpopulations poses a number of challenges to the practice of cancer research, including the design of reproducible and meaningful experiments. Tumor heterogeneity also has significant consequences for the clinical assessment of tumor prognosis and the development of effective treatment regimens.

Increased metastatic ability and bone formation of a mammary adenocarcinoma in vivo after in vitro passaging

On in vitro passaging of the rat mammary adenocarcinoma R3230AC cell line, phenotypic changes occurred that were expressed in vivo. The histology of this mammary adenocarcinoma changed to a fibrosarcoma and then to an osteosarcoma. The overall population of early passaged cells consisted of a mixture of predominantly epithelial-like cells and few fibroblast-like cells; however, later passaged cells consisted more of the latter type. Along with the changes in histology, the tumor line also became highly metastatic in animals after in vitro passaging. The etiology of these phenotypic changes was not determined. Cytogenetic studies revealed chromosome changes in cells of later passages. Cells of 90 or greater passages that produced bone tumors were found to have fewer chromosomes and a metacentric marker isochromosome. In this report a correlation is made between the aberrant change in histology, increased metastatic ability and the presence of a marker chromosome of the R3230AC tumor.

Chromosome counts of 90Sr-induced osteosarcomas in mice. IV. Variation of chromosome counts when using tumours of predetermined age for transplantation

Transplanted tumours from a 90Sr-induced primary tumour were used as an experimental model to eliminate any connection between the chromosome distribution and outgrowth period of radiation-induced transplanted tumours. For this reason repeated transplantations were performed from different tumours of predetermined age from a transfer generation, to receive separate but parallel transfer generations. From each one of these generations a tumour of the same age as used to establish a particular generation was used for continued transplantation. It was then observed that the percentage of 40-chromosome cells in general decreased with the age of the tumour used for transplantation. Furthermore, early established transfer generations were often characterized by more slow growing tumours. However, it should be realized that even if a true relationship between chromosome pattern and outgrowth period cannot be eliminated, the differences found may be due to accidental variations.