Preoperative diagnosis of multiple primary malignant neoplasm in gastrointestinal and breast cancers: Impact of FDG-PET/CT

Objective: The reports of multiple primary malignant neoplasm (MPMN) have increased due to the development of imaging technologies that have influenced the extension of the 5-year relative survival rate for all cancers. Integrated positron emission and computed tomography (PET/CT) with 18F-fluorodeoxyglucose (FDG) has shown its advantages for detecting, staging, evaluating the prognosis, and offering better insights for survivors, their families and physicians. The aim of this study was to retrospectively investigate the impact of whole-body FDG-PET/CT in detecting MPMN during the initial staging work-up of gastrointestinal and breast malignancy, and to describe their characteristics. Methods: The cases were identified by reviewing the Dokkyo Medical University Hospital PET Center's database, searching for patients referred from the Department of Surgical Oncology and the Department of Gastroenterological Surgery, who underwent preoperative staging with whole-body FDG PET/CT at our center between January 2007 and December 2009. A total of 778 patients matched these criteria. Of them, 40 PET/CT reports mentioned suspicious cases of MPMN. The medical records of these 40 cases were retrieved and examined. The follow-up data of these patients was reviewed until February 2010. Results: Of 778, 32 patients were diagnosed with additional unexpected cancers, which 27 (3.5%) were incidental double cancers and 5 (0.64%) had triple primary lesions. Overall 37 MPMN, twelve corresponded to stage 0, nineteen to stages I-II, three to stages III-IV, and three remained uncertain. Sensitivity and positive predictive value of FDG PET/CT in detecting a controversial lesion were 76.5 and 70.3, respectively. The colorectum was the most common site for synchronous MPMN (17 of 37 cancers; 45.9%), followed by stomach (9:24.3%), prostate (3:8.1%), thyroid (38.1%), breast (25.4%), biliary duct (1:2.7%), kidney (1:2.7%), and lung (1:2.7%). Conclusions FDG PET/CT was useful for finding multiple primary malignant neoplasm with a relatively high sensitivity. Physicians should pay special attention to rule out the presence of unexpected additional primary lesions in initial staging work-up for colorectal cancer.