A series of experiments is described in which fragments derived from two mammary tumors of distinct types were transferred at different developmental stages to the anterior chamber of the eye of normal rabbits. It was found that the ability to survive and to grow progressively after transplantation was not immediately related to anaplastic cellular changes. On the other hand, there existed a definite correlation between the success of transplantation and the morphological relationship of tumor cells and the normal cells of the host. Transplantation to normal animals could not be effected during stages of local tissue invasion but was successfully performed as soon as the tumor cells manifested the ability to invade foreign tissues or to metastasize in the spontaneous host. It was concluded, therefore, that neither anaplasia nor local tissue invasion represented autonomy but, rather, stages in its development and that the final attainment of this condition was only evidenced by metastasis or by invasion in foreign tissues.

The tumors were successfully transplanted to normal animals during this series of experiments and have been carried by serial transfer to the present time. The most outstanding feature in the transplantation of the papillary type tumor was the marked difference in susceptibility exhibited by the two sexes. The acinar type tumor was distinguished by high transplantability, an extremely rapid growth rate and early regression.

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