De Novo Presentation of Sarcoidosis on Restaging FDG PET/CT in Rectal Carcinoma With Self-resolution.

Sarcoidosis is a systemic disorder of unknown etiology characterized by development of noncaseating granulomas in more than 1 organ system. Development of sarcoidosis during or immediately after chemotherapy and immunotherapy is not uncommon. We present a 61-year-old woman in whom restaging F-FDG PET/CT detected asymptomatic sarcoidosis after neoadjuvant chemoradiotherapy for carcinoma rectum, which resolved spontaneously by the end of adjuvant chemotherapy with no specific treatment. Recognition of anatomic-metabolic pattern of sarcoidosis could prevent erroneous upstaging of the primary malignancy during restaging PET/CT following chemotherapy, and such lesions may show self-resolution.