Nearly half of<unk>  cases occur in the setting of coexisting differentiated thyroid cancer. This suggests that many<unk>  cases have dedifferentiated from differentiated thyroid cancer and, as a result, become more aggressive and difficult to treat. Differentiated thyroid cancer is seen coexisting with<unk>  on fine-needle aspiration biopsies in 20-50% of cases.<unk>  tumors have a high mitotic rate and frequently invades the local blood and lymphatic vessels. Cellular death is frequently visualized on microscopic images. The presence of regionally swollen lymph nodes in older patients in whom needle aspiration biopsy reveals characteristic vesicular appearance of the nuclei supports a diagnosis of<unk>  carcinoma. Microscopic images of<unk>  usually show inflammatory cells from the immune system such as T cells and macrophages. On immunohistochemistry testing,<unk>  is usually positive for the keratin, p53, and PAX8 proteins and is negative for thyroid transcription factor-1, thyroglobulin, and calcitonin.<unk>  cells demonstrate high levels of PD-L1 expression. BRAF and TERT mutations are seen more commonly in<unk>  than in differentiated thyroid cancer.
Anaplastic thyroid cancer
Thyroid lymphoma
Follicular thyroid cancer
Papillary thyroid cancer
Medullary thyroid cancer
Squamous-cell thyroid carcinoma
Poorly differentiated thyroid cancer
Thyroid adenoma