Anaplastic Thyroid Cancer, from the CureRays guide library.

Anaplastic thyroid cancer is a rare, fast-growing thyroid cancer that requires urgent, coordinated treatment — and new targeted drugs matched to its genetics are improving outcomes for some patients.

What it is.

Anaplastic thyroid cancer is a rare and aggressive cancer of the thyroid, the butterfly-shaped gland in the front of the neck that controls metabolism. Unlike the far more common and very treatable differentiated thyroid cancers (papillary and follicular), anaplastic thyroid cancer grows rapidly, often appearing as a quickly enlarging neck mass that may cause hoarseness, trouble swallowing, or difficulty breathing as it presses on the windpipe and voice box. It tends to occur in older adults and is considered a medical urgency — evaluation and treatment need to begin quickly. Importantly, anaplastic thyroid cancer does not take up radioactive iodine the way differentiated thyroid cancers do, so the iodine treatment used for those cancers does not work here; instead, treatment relies on a combination of surgery (when possible), external-beam radiation, chemotherapy, and increasingly, targeted drugs chosen based on the tumor's genetic makeup. A major advance in recent years is the discovery that a portion of these cancers carry a specific gene change (a BRAF mutation) that can be treated with targeted pills, sometimes shrinking tumors enough to allow surgery. Because care must be fast and coordinated, anaplastic thyroid cancer is best managed by an experienced multidisciplinary team, and clinical trials are an important option.

How radiation treats it.

Radiation uses focused high-energy beams to damage the DNA inside cancer cells so they can no longer grow and divide. In anaplastic thyroid cancer, radiation plays a central role because this cancer grows quickly in the neck and threatens vital structures such as the windpipe, voice box, and swallowing muscles. Radiation is used to control the cancer locally — shrinking it, relieving or preventing pressure on the airway, and reducing the chance it regrows in the neck — and it is frequently combined with chemotherapy or given after surgery. Modern techniques such as IMRT shape a high dose tightly around the tumor while sparing the spinal cord and as much of the swallowing and breathing structures as possible. A particularly hopeful development is that for tumors with a BRAF mutation, targeted pills can shrink the cancer first, after which radiation and surgery can consolidate that response. Because timing matters in this fast-moving disease, radiation is often started promptly and coordinated closely with the rest of the team. When the focus is comfort, shorter palliative courses of radiation can quickly ease pain, pressure, and breathing or swallowing problems. Your radiation oncologist will tailor the dose and technique to the goal of care — whether aggressive control or symptom relief — and to protecting the structures of the neck.

The ways we can treat it.

Intensity-modulated radiation therapy (IMRT). IMRT delivers a high, shaped dose to the cancer in the neck while sparing the spinal cord, swallowing structures, and airway as much as possible — important when treating a tumor close to vital structures.

Concurrent chemoradiation. Radiation combined with chemotherapy can improve local control of this fast-growing cancer and is a common approach when the goal is aggressive treatment of disease in the neck.

Radiation after targeted-drug response. When targeted pills shrink a BRAF-mutated tumor, radiation (often with surgery) is used to consolidate that response and control the cancer in the neck.

Palliative radiation. When the priority is comfort and airway protection, shorter courses of radiation can quickly relieve pressure, pain, and breathing or swallowing difficulty.

Questions we hear often.

Why won't radioactive iodine work for this cancer? Radioactive iodine treats the common, slower thyroid cancers because their cells absorb iodine. Anaplastic thyroid cancer cells have lost that ability, so iodine treatment does not work. Instead, treatment relies on external-beam radiation, surgery, chemotherapy, and targeted drugs.

Why is genetic testing of the tumor so important and so urgent? A portion of anaplastic thyroid cancers carry a BRAF mutation that can be treated with targeted pills, which sometimes shrink the tumor enough to allow surgery. Because the cancer grows fast, testing the tumor's genetics quickly lets the team start the most effective treatment without delay.

Should I consider a clinical trial? Yes — clinical trials are an important option in anaplastic thyroid cancer and may provide access to newer targeted and immune therapies. Ask your team whether a trial is appropriate for your situation; acting quickly is important with this diagnosis.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.