18F-FDG PET/ct-positive internal mammary lymph nodes: Pathologic correlation by ultrasound-guided fine-needle aspiration and assessment of associated risk factors

Abstract

OBJECTIVE. Metastatic breast cancer in internal mammary (IM) lymph nodes is associated with a poor prognosis. This study correlates 18F-FDG PET/CT-positive IM lymph nodes with ultrasound-guided fine-needle aspiration (FNA) cytopathologic results and determines risk factors for IM node positivity on PET/CT. MATERIALS AND METHODS. For this retrospective study, a database search was performed to identify patients referred for whole-body 18F-FDG PET/CT for initial staging or restaging of breast cancer from January 1, 2005, through December 31, 2010. The radiology reports and images were reviewed for patients with 18F-FDG-avid IM lymph nodes on PET/ CT and correlated with the cytopathologic results from FNA of selected PET/CT-positive IM lymph nodes. The patients with positive IM nodes on PET/CT who underwent PET/CT for initial staging were compared against age-matched and tumor size-matched patients to identify risk factors for IM node positivity on PET/CT. RESULTS. One hundred ten of 1259 patients (9%) had an 18F-FDG-avid IM lymph node on PET/CT. Twenty-five patients underwent ultrasound-guided FNA of a suspicious IM node, and 20 IM lymph nodes (80%) were cytologically proven metastases from the primary breast malignancy. High tumor grade, the presence of lymphovascular invasion (LVI), and triple receptor-negative hormonal receptor status were found to be significant risk factors for IM node positivity on PET/CT (p < 0.05). CONCLUSION. Although fewer than 10% of breast cancer patients have positive IM nodes on 18F-FDG PET/CT performed for initial staging or restaging, a positive IM node indicates a very high likelihood of malignant involvement on ultrasound-guided FNA. The presences of high tumor grade, LVI, or triple receptor-negative status are risk factors for IM node positivity on 18F-FDG PET/CT. © American Roentgen Ray Society.