Malignancies of the thyroid gland

Papillary carcinoma is by far the most common thyroid malignancy and has an excellent prognosis. It spreads through lymphatics to cervical nodes and is diagnosed on nuclear features rather than architecture: ground-glass "Orphan Annie eye" nuclei, nuclear grooves, and psammoma bodies. Prior ionizing radiation exposure to the head and neck is its best-established risk factor.

Follicular carcinoma spreads hematogenously to bone and lung and cannot be distinguished from a benign follicular adenoma on fine-needle aspiration, because the diagnosis depends on demonstrating capsular or vascular invasion in the resected specimen. Medullary carcinoma arises from parafollicular C cells rather than follicular cells, secretes calcitonin, and shows amyloid deposits in its stroma; it occurs sporadically or as part of MEN 2A and MEN 2B, which are associated with RET proto-oncogene mutations. Anaplastic carcinoma is an undifferentiated tumor of older adults that grows rapidly, invades local structures causing hoarseness and airway compromise, and carries a very poor prognosis.

Evaluation of a thyroid nodule generally begins with serum TSH and ultrasound; fine-needle aspiration is the key diagnostic step for suspicious nodules. Most thyroid cancers are euthyroid at presentation, so normal thyroid function tests do not rule out malignancy. Treatment is usually surgical, with radioactive iodine used for differentiated (papillary and follicular) tumors that take up iodine, followed by thyroid hormone replacement.

USMLE Step 1 tests thyroid malignancies within endocrine pathology, favoring the histologic and genetic associations that let you identify each type from a vignette. The PTCE approaches the thyroid from the medication side, covering the drugs used for thyroid disorders and hormone replacement after thyroid surgery.