An Unexpected Finding of Poorly Differentiated Thyroid Carcinoma in a Toxic Thyroid Nodule

Poorly differentiated thyroid carcinoma (PDTC) is a rare entity of thyroid cancer with an intermediate clinical behavior between differentiated and anaplastic thyroid cancer. Here we present a patient who was referred to the endocrinology clinic for evaluation of hyperthyroidism and multinodular goiter. Due to presence of right toxic thyroid nodules and compressive symptoms, the patient underwent right lobectomy and isthmectomy, where surgical pathology revealed PDTC in the right thyroid lobe. Based on this unusual case of malignancy within a toxic nodule, we propose further evaluation of hot nodules with concerning features such as growth rate. Furthermore, exploration of relative sodium iodine symporter (NIS) expression in PDTC may help us better understand how iodine uptake changes as PDTC develops, which may impact our approach to assessing and treating PDTC in the future.