ALK-positive Histiocytosis Mimicking Colon Cancer on 18 F-FDG PET/CT.

As a subtype of histiocytic neoplasm, ALK-positive histiocytosis is rare, especially with colorectal involvement. We herein describe 18 F-FDG PET/CT findings of ALK-positive histiocytosis with colon involvement in a 33-year-old man. The PET/CT scan demonstrated intense FDG uptake in the colonic lesion, along with multiple hypermetabolic lymph nodes. The colon cancer with lymph node metastases was initially suspected; however, the final pathological findings confirmed the diagnosis of ALK-positive histiocytosis.