Differentiated thyroid cancer is treated by surgery, radioiodine treatment, and Thyroid Stimulating Hormone (TSH) suppression. The role of external beam radiotherapy is mainly palliation of radio-iodine non avid metastatic lesions and in inoperable tumors. Metastasis involving weight-bearing bones and vertebral metastasis with impending spinal cord compression are primarily treated by external radiation. External Beam Radiotherapy improves loco-regional control in patients with gross residual disease after surgical resection. Patients with extra-thyroidal disease and positive margins are treated by adjuvant external beam radiotherapy, especially when the post op radio-iodine scan is negative. External beam radiotherapy is the treatment of choice for radio-iodine non avid inoperable loco-regional recurrence. SRS alone or surgery followed by SRS is the preferred treatment for solitary brain metastasis. Whole brain radiotherapy is the treatment of choice for multiple brain metastatic disease.

The standard treatment for patients with differentiated thyroid cancer (DTC) is a combination of surgery, radioactive iodine (RAI), and long-term thyroid hormone–suppression therapy. Treatment of patients whose diseases persist, recur, or metastasize remains a challenge. The role of cytotoxic chemotherapy in the treatment of thyroid cancer is limited. The key signaling pathways involved in the pathogenesis of thyroid cancers are the RAS/RAF/MEK & PI3K/Akt/mTOR pathways. Systemic therapy in thyroid cancer involves the use of tyrosine kinase inhibitors targeting the above mentioned pathways which are often both effective in controlling disease and have manageable toxicity. Sorafenib and lenvatinib are approved for advanced radioiodine refractory and poorly differentiated thyroid cancers and vandetanib and cabozantinib for recurrent or metastatic medullary thyroid cancers. Cabozantinib is also approved for the treatment of locally advanced or metastatic radioactive iodine–refractory differentiated thyroid cancer that has progressed after prior VEGF-targeted therapy. The combination of dabrafenib (BRAF inhibitor) and trametinib (MEK inhibitor) is approved for BRAF V600E mutated unresectable locally advanced anaplastic thyroid cancer. Selpercatinib, RET kinase inhibitor is used for advanced and metastatic RET mutated medullary thyroid cancers and advanced and metastatic RET fusion-positive thyroid cancers of any histologic type. Various clinical trials using newer molecules targeting the aforementioned pathways are ongoing.

Anaplastic carcinoma thyroid, also known as undifferentiated thyroid carcinoma, is a rare but highly aggressive malignant tumor, which accounts for 2–3% of all thyroid malignancies. It is mostly seen in elderly females in their 6th or 7th decade. It carries a very bad prognosis with an average median survival of 5 months. Patients often present with a rapidly growing, painful, woody hard lower anterior neck mass fixed to underlying structures. In addition to local invasion, patients also present with regional nodal spread and distant metastasis. Though the risk factors for anaplastic carcinoma thyroid are unknown, most of them develop in the setting of long-standing goiter, possibly in an undiagnosed, well-differentiated thyroid carcinoma. Management of anaplastic carcinoma thyroid demands a multidisciplinary approach with the involvement of surgeon, radiation oncologist, radiologist, and endocrinologist. The conventional treatment of anaplastic carcinoma thyroid includes surgery, radiation, and chemotherapy. Recently, multitarget tyrosine kinase inhibitors are also incorporated into the treatment. However, prognosis of the disease is very poor with 4 months of overall survival of 35% and overall disease-specific mortality of 98–99%. In this chapter, we discuss how to approach the condition and various treatment strategies to provide improved treatment outcomes for patients diagnosed with anaplastic carcinoma thyroid.