Anaplastic Thyroid Carcinoma With Horner Syndrome and Unusual Metastasis Reveals Masked Papillary Thyroid Carcinoma Following Neoadjuvant Therapy

This case is a unique depiction of how ATC can present despite uncharacteristic immunohistochemical markers, secondary symptoms, and hidden comorbidities. As an understudied malignancy, it is important to recognize this condition's variability to prevent increased mortality and morbidity.