Metachronous Adenocarcinoma of the Lung in the Setting of Metastatic Gastric Neuroendocrine Tumor: Value of Elucidating Discordance on Dual-Tracer PET/CT with Ki-67 Index.

Dual-tracer PET/CT (F-FDG and Ga-DOTATATE) has become established practice in the management of metastatic neuroendocrine neoplasms (NENs) and has demonstrated the advantages to patient management of deciphering the molecular PET characteristics of the tumor. Judicious elucidation of the findings is important, especially in scenarios of discordance with reported histopathology, potentially leading to an unsuspected diagnosis such as second primary malignancies. Such a diagnosis established early in the disease course, and mostly at an asymptomatic stage, provides lead time for timely, appropriate management. This concept was elaborated in a case of incidentally detected F-FDG-avid metachronous lung adenocarcinoma in a patient with metastatic, well-differentiated gastric NEN, wherein dual-tracer PET/CT showed F-FDG-avid but not Ga-DOTATATE-avid lung opacity.