Regional differences in tumor growth: Studies of the vascular system

We have previously shown that tumor cells inoculated into the thoracic region of the trunk grow much more rapidly and with a higher frequency than do an equivalent number of cells injected more posteriorly. We thought that these results might have been a reflection of an underlying difference in the vascular system supplying these regions of the trunk. The present experiments which were undertaken to characterize various aspects of the vascular system associated with the transplantation sites used in these studies include measurements of rates of diffusion of salt solutions, of protein clearance, and of the retention of radio‐labelled cells and cellular debris. We have examined local differences in temperatures and studied the effect of change of ambient temperature on those local differences as well as on tumor growth. More directly, we have measured blood flow to the capillaries by intracardiac administration of radioactive microspheres, and assessed the ability of inoculated tumor cells to induce angiogenesis. We have been unable to detect any major differences in the parameters of the vascular system that we have analyzed. Thus we cannot offer any satisfactory explanation for the observed four‐fold differences in tumor growth in anterior vs posterior inoculation sites. The results are discussed in terms of underlying developmental gradients which can be invoked to provide a basis for further experimentation.