Malignant follicles of a differentiated thyroid carcinoma releasing iodinated thyroglobulin into the lymphatic vessels.

Serial sections across a follicular thyroid carcinoma taken from a 71-year-old woman with hyperthyroidism and grossly elevated serum thyroglobulin were examined by PAS staining and autoradiographic techniques. PAS positive material, presumably thyroglobulin, was found in the interstitial network between follicles. Some of this material was autoradiographically positive for 125I within 17 h after tracer application. Direct connections between the lumina of tumour follicles and the lymphatic vessels surrounding them were identified. These channels can explain the release of iodinated thyroglobulin by some differentiated carcinomas.