Growth, morphology, and function of xenotransplanted human tumors

Tansplantability, growth, morphology, and function of xenotransplanted human tumors, such as carcinomas of the lung, liver, breast, choriocarcinoma, and blastomas of the liver, lung, kidney, and uterus, are described. From the tumor take rate, it is clear that xenotransplantation cannot be used for the study of every human tumor: slow-growing tumors are difficult to analyze, and functioning adenomas and low-grade malignant carcinomas are at present almost impossible to study by this approach. From the authors' transplantation experience, tumor antigenicity to nude mice with no T-cell function, either tumor specific or species specific, was suspected. Therefore, the growth in nude mice may not equate to that in the human body. The stroma of the transplanted tumor, which is most likely of mouse origin, might also alter the growth rate, as it did the histology of some tumors. Another possible hindrance that has not been described in the text is the mouse endogenous virus. Serially transplanted human tumors are often infected with C particles, which could well influence the tumor growth and character. In spite of the presence of some factors unfavorable for the study of human tumors through xenotransplantation, it has, nevertheless, been clearly shown that the nude mouse/human tumor system is a very useful tool for functional analysis of tumors in relation to growth, differentiation, and morphology, such as eutopic or ectopic production of various hormones, AFP, normal serum proteins, colony-stimulating factor, erythropoietin, and so on. This system can be employed to elucidate the production of many other biologically active and inactive substances by a variety of tumors and their effects on the host in the future and should provide better understanding of human cancers. Attempts to induce differentiation and to change the biologic behavior of xenotransplanted human malignant tumors have failed so far, except for induced dormancy of breast carcinoma under unfavorable hormonal conditions. This line of investigation may have particular import on cancer research, particularly in relation to the biology and treatment of human cancers.