What is the most common malignant tumor of the thyroid gland?

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Papillary carcinoma is the most common thyroid malignancy, accounting for the majority of thyroid cancers. It arises from follicular cells and tends to spread first through the lymphatic system to regional cervical nodes, which explains why nodal involvement is frequently seen even when the primary tumor is small. This tumor generally has an excellent prognosis with appropriate treatment, such as thyroidectomy often followed by radioactive iodine. Histologically, you’ll see papillary fronds with fibrovascular cores, nuclear grooves and clearing (the so-called Orphan Annie eye nuclei), and psammoma bodies. It most often affects younger patients and can be associated with prior neck irradiation. In contrast, medullary carcinoma comes from parafollicular C cells and is less common; follicular carcinoma tends to spread hematogenously; anaplastic carcinoma is rare and highly aggressive.