Vascular dissemination of tumor cells in relation to temperature-dependent metastasis in frogs

Metastasis is a temperature-related phenomenon in the North American leopard frog (Rana pipiens) affected with the Lucké renal adenocarcinoma. The frog is a poikilothermic vertebrate whose internal body temperature closely follows that of the environment, and tumor-bearing frogs living in a warm (28 degrees C) environment have a much higher incidence of metastasis (greater than 75%) than those in cold (4 degrees C) conditions (less than 6%). In this investigation it was found that Lucké tumor cells labeled with fluorescein isothiocyanate could be detected in frozen sections of all organs examined within 15 minutes, regardless of whether the hosts were adapted to a warm or a cold environment. Separate experiments involving inoculation of isotope-labeled tumor cells demonstrated that large numbers of cells arrived in the liver and other organs of animals kept at either end of the temperature range. These findings show that the infrequency of metastasis by Lucké adenocarcinomas in chilled frogs is not due to failure of dissemination of tumor cells consequent upon temperature-mediated changes in blood viscosity or flow patterns. Thus they establish the important baseline that the effects of temperature on metastasis in this vertebrate are exerted directly on the tumor cells and/or the internal environment of the host and that the system therefore provides new opportunities for probing the biology and biochemistry of tumor metastasis.