Which thyroid carcinoma type does not concentrate iodine?

Anaplastic thyroid carcinoma is characterized by its aggressive behavior and lack of differentiation, which leads to its inability to concentrate iodine. Unlike other types of thyroid cancer, such as papillary and follicular carcinomas that arise from follicular cells and can uptake iodine due to their ability to maintain some normal thyroid function, anaplastic carcinoma loses these characteristics. As a result, it does not effectively absorb iodine, making it resistant to iodine-based imaging and treatment modalities commonly used for differentiated thyroid cancers.

Medullary thyroid carcinoma, which arises from parafollicular C cells, also does not concentrate iodine as it originates from a different cell type altogether. However, in this context, the anaplastic carcinoma's lack of iodine uptake is more prominent due to its highly undifferentiated nature and aggressive clinical course, which are the key identifiers of this malignancy. Consequently, anaplastic thyroid carcinoma stands out specifically for its inability to concentrate iodine compared to the other thyroid carcinoma types mentioned.