On the Kinetic and Invasive Power of Regenerating Tissue and on Similarities in the Behavior of Thyroid Transplants and Carcinomas

Abstract

The following observations are of interest because they clearly demonstrate that some of the fundamental characteristics of cancerous growth can be found in regenerative growth. In addition, they bring out very sharply some of the factors which, under ordinary conditions, restrain regenerative proliferation. I. INVASION OF BLOOD VESSELS BY REGENERATING THYROID TISSUE In the course of a study of the factors which determine regeneration of the thyroid gland and the fate of thyroid transplants, we compared autotransplantation of one thyroid lobe in cases in which the second lobe had been left intact and in which it had been extirpated previous to the transplantation. We also compared the fate of autotransplants and homoiotransplants at various stages. In an animal, a female guinea-pig (no. 758) weighing 370 grams, we transplanted one lobe of the thyroid subcutaneously into the same animal. The lobe of the other side was left intact. Seven days later the transplant was taken out for examination. The recovered piece was relatively large and cut into serial sections. Microscopic examination showed the following: A connective tissue capsule rich in fibroblasts surrounds the piece; it encircles a ring of acini, which, however, is not complete, being interrupted at such places where fat tissue constituted the periphery of the transplant. The peripheral acini are the largest ones; they contain often well formed colloid. Other acini are filled with blood and a few contain some polynuclear leucocytes. Towards the center the acini become smaller, and especially is their lumen diminished. At various places the inner acini seem to end in cell strands without lumen. These cell strands accompanied by growing fibroblasts grow towards the center of the piece, which latter consists in the main of thyroid tissue which, being deprived of blood supply after transplantation, had become necrotic and in part hemorrhagic. In the necrotic walls of the central necrotic acini some disintegrating polynuclear leucocytes are seen. In one small area of the necrotic center a somewhat larger collection of disintegrating polynuclear leucocytes can be observed. The acini as well as the more centrally situated epithelial strands contain relatively frequent mitoses. In the peripheral concentrically arranged capsule of connective tissue we find some thyroid tissue in the form of extensive ducts; they may send off branches in various directions. On the whole they follow the direction of the connective tissue capsule in which they are embedded. These ducts are perhaps acini which regenerated in the connective tissue capsule, and under the influence of the growing connective tissue assumed a concentric growth similar to that of the connective tissue itself. Mitoses are also found in these ducts. They are situated in the periphery of the ring of acini. There is on the other hand a possibility that they took their origin in epithelial ducts which occur even in the normal thyroid.