Data bearing on the occurrence and distribution of metastases, as recorded in the preceding papers of the series, are analyzed with reference to the parts played by the tumor cell and by conditions which influence cell distribution and cell growth.
It is shown that, while the tumor cell is an essential element in the production of metastases, its influence is relatively constant, and that the prime factors responsible for variations in the occurrence and distribution of metastatic growths are conditions that influence cell distribution or that affect the viability of the cell during transport, and conditions that affect the nutrition of the cell wherever it may become lodged.
It is further shown that both the presence and the absence of metastases, as well as peculiarities of distribution and of growth, are susceptible of a comparatively simple explanation upon the basis of well recognized principles of pathological action. In brief, it was found that, while the tumor cells might be distributed by either the blood stream or the lymphatics, the mode of distribution and the fate of the cells were determined in accordance with the same general principles that are applicable to the distribution and disposal of foreign cells introduced into the animal body. It was pointed out, however, that in applying these principles to tumor metastasis, it was necessary to recognize the fact that tumor cells bear a definite relation to the tissues of the host and that they are living and agressive agents. Hence, the reaction that they arouse differs in some respects from that produced by inert or unorganized foreign material or by living cells of a foreign species.
Activated tumor cell integrin αvβ3 cooperates with platelets to promote extravasation and metastasis from the blood stream