Recurrent Poorly Differentiated Thyroid Cancer Successfully Treated With Radiation and Immunotherapy.

A 65-year-old patient presented with recurrent, locally advanced poorly differentiated thyroid cancer despite 2 neck surgeries, and with newly diagnosed brain and skull base metastases. He was treated with palliative stereotactic radiosurgery to the brain and skull base lesions. Thereafter, as no targetable genetic alteration was identified and antiangiogenic multikinase inhibitors were deemed at high risk of hemorrhagic complications, off-label systemic therapies were considered. The mechanistic target of rapamycin (mTOR) inhibitor everolimus could not be obtained due to lack of insurance coverage, so the patient was treated with single-agent pembrolizumab. He showed an initial remarkable response, but unfortunately had disease progression in the neck and upper mediastinum after 1 year of therapy. At that time, he was treated with external beam radiotherapy, with concomitant pembrolizumab. He was then found to have an CTSB::ALK fusion, which has previously been described in 2 cases of thyroid cancer. However, as he showed a positive response to radiation with pembrolizumab, he continued single-agent immune checkpoint inhibition and had a persistent marked response almost a year after completing radiation. The patient was then followed at an outside institution and was transitioned to hospice at time of progression per his preference. He died 4 years after his initial diagnosis.