The role of PET-CT in the diagnosis of multiple primary malignant neoplasms

Multiple primary malignant neoplasms (MPMN) are defined as the presence of two or more unrelated tumors, which occur simultaneously or successively in one or more organs of the same host. They are classified as synchronous or metachronous depending on the time interval between the appearance of the first and second tumor: synchronous in the case of simultaneous appearance or in the following 6 months, and metachronous when the second tumor appears later than six months with respect to the first. The majority of MPMN consists of the presence of two tumors, with the presence of three or more neoplasms being rare. The most frequent sites for the development of multiple malignant tumors are the organs of the digestive system, the lung and the breast. Because the prognosis of patients with synchronous tumors is better than the presence of a tumor with metastasis, their differentiation is of vital value. The positron emission tomography-computed tomography with 18F fluorodeoxyglucose (18F-FDG/PET-CT) represents the ideal method for the detection of NMPM. It allows evaluation of the known tumor and its characteristics; and makes it possible to detect unsuspected lesions, often asymptomatic, expressed as hypermetabolic lesions. The objective of this paper is to analyze and review MPMN and the usefulness of 18F-FDG/PET-CT for their diagnosis.