CARCINOMA OF THE THYROID GLAND, WITH SPECIAL REFERENCE TO A CLINICOPATHOLOGIC CLASSIFICATION*

Abstract

FROM the clinical point of view carcinomas of the thyroid can be divided into two main groups, the papillary and the nonpapillary. Papillary carcinomas behave as lymphangioinvasive tumors and metastasize to lymph nodes, whereas nonpapillary carcinomas are hemangioinvasive and metastasize through the blood stream. The great differences in the clinical behavior and prognosis of these two groups of tumors can be explained by their respective tendencies to invade lymphatics and blood vessels. Papillary carcinomas tend to be nonencapsulated, or at least nonenucleable. If a capsule is present it is formed by sclerosis and is densely adherent to the surrounding thyroid tissue so that it cannot be “shelled out” like the differentiated nonpapillary carcinomas. It is perhaps because the papillary carcinomas originate in the parenchyma of the thyroid, which is well supplied with lymphatic vessels, that they tend to invade lymphatics. If the nonpapillary tumors arise in adenomas the absence or paucity of lymphatics in these adenomas may explain their tendency to invade blood vessels rather than lymphatics.