Abstract
Summary
The vascular supply of the grossly viable portions of grafts of the MTG-B mouse mammary carcinoma was measured with 59Fe-labeled red cells. The relative vascular space was constant, estimated as 1.5 X 10-2 μl/mg in tumors yielding 50 to 1900 mg of “cleaned” tissue from which necrotic, cystic, or hemorrhagic areas had been removed. We have previously reported that the potential growth rate in the grossly viable portions of MTG-B tumors is also constant from the time tumors are small until near death of the host animals. It is postulated that an equilibrium between the viable portions of such tumors and their vascular supply is established when tumors are small. This equilibrium persists well into the period when tumors are large; and necrosis, hemorrhage, and cysts are common. It is thus further suggested that such degenerative changes become marked when the absolute number of new tumor cells born exceeds the capacity for new vascular tissue formation. However, the functional vascular supply of the regions from which most, if not all, new cells arise in large tumors of this type is apparently adequate to support the same metabolic and proliferative rates as in small tumors, despite the occurrence of widespread degeneration in adjacent areas. Insofar as the response to therapy depends on the relative vascular supply and proliferative rate, the sensitivity per unit viable tissue would be expected to be similar in large and small tumors of this type.
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