A 74-year-old man underwent excisional biopsy of an anterior mediastinal mass that revealed squamous cell carcinoma of thymic origin. Immunohistochemistry revealed insulin-like growth factor-1 receptor positivity, which has been associated with worse prognosis. Restaging FDG PET/CT revealed extensive soft tissue and osseous metastases despite surgery and chemoradiation therapy. Patient was then enrolled in a clinical trial with anti-insulin-like growth factor-1 receptor therapy. A 3-month follow-up FDG PET/CT showed disease progression with an increase in size and number of hypermetabolic metastatic lesions, including interval development of multiple new metastases.