What type of spread is most commonly associated with thyroid metastasis?

Thyroid metastasis is most commonly associated with hematogenous spread. This is due to the rich vascular supply of the thyroid gland, which allows cancer cells to enter the bloodstream more easily and reach distant organs. Many thyroid cancers, especially papillary and follicular carcinoma, can spread through the bloodstream to regions such as the lungs and bones.

Lymphatic spread, while also possible in thyroid cancers, is more characteristic of other cancers such as breast or lung cancer. Direct invasion refers to the local extension of the tumor into adjacent tissues and is not the primary method of metastasis for thyroid cancers. Transcoelomic spread typically involves dissemination through body cavities, which is more representative of cancers affecting organs within the coelomic space, such as the ovaries. Thus, hematogenous spread is the key mechanism for the metastasis of thyroid cancers into distant sites.