Lung Adenocarcinoma Staged as an Unknown Primary Presenting with Symptomatic Colon Metastases: Staging by 18F-FDG PET/CT.

A 66-year-old man, who presented with bright red blood per rectum, was referred for an (18)F-FDG PET/CT after colonoscopy showed two suspicious colon masses, which were biopsied to reveal an adenocarcinoma of unknown origin. PET/CT showed two intensely FDG-avid colon masses as well as an unsuspected FDG-avid lung mass, which was biopsied to reveal a primary lung adenocarcinoma. Immunohistochemistry confirmed the two colon metastases were of pulmonary origin. It is extremely rare for lung carcinoma to present with symptomatic colon metastases, with only 11 cases described in the literature. We report the first case of the utility of (18)F-FDG PET/CT in staging a patient who presented with symptomatic colon metastases of an unknown primary lung malignancy.