Comparison of Natural and Artificial Lung Metastases from a Murine Tumour of Spontaneous Origin

Abstract

The metastatic potential of the non-immunogenic CBA SA F tumour was investigated. Eradication of subcutaneous tumours of different sizes with 80Gy of X-rays resulted in lung metastases incidence increasing from 0 to 100% as the primary tumour size increased from 2 to 10mm. The number of metastases also increased and the average survival time decreased with increasing primary tumour size at treatment. The survival times suggested slower growth in lungs compared with subcutaneous sites. A bioassay for circulating tumour cells indicated there were less than 30 cells per ml venous blood in mice with tumours less than 12mm in diameter.

Experiments on ‘artificial’ metastases showed that lung colonies after intravenous injection of SA F cells had a higher colony forming efficiency and appeared later after smaller inocula. The difference in appearance times plus the observation of a wide range of colonies in the same lung for both natural and artificial metastases suggest a) a wide range of growth rates, or b) a multicell origin for some colonies, or c) a dormant period for some colonies. Correlations of these kinetic differences with treatment sensitivity are being investigated.