What specifically characterizes medullary carcinoma of the thyroid?

Medullary carcinoma of the thyroid is specifically characterized by the presence of amyloid stroma. This amyloid deposition is derived from the calcitonin produced by the C cells, also known as parafollicular cells, of the thyroid gland. The presence of this amyloid substance is a distinctive histopathological feature that can help differentiate medullary thyroid carcinoma from other types of thyroid cancers.

Additionally, this type of cancer typically originates from the neuroendocrine cells, which also contribute to the production of calcitonin. Although high calcitonin secretion is an important aspect of the disease, the defining feature is the presence of amyloid in the stroma when assessed histologically. Therefore, identifying the amyloid stroma in tissue samples is crucial for diagnosis.

While encapsulation may be a feature of some well-differentiated thyroid tumors, it is not as characteristic of medullary carcinoma. Furthermore, while medullary carcinoma can show metastasis, particularly in advanced stages, the lack of metastasis is not a defining characteristic of this tumor type.