Department of Nuclear Medicine, Dongsan Medical Center, Keimyung University School of Medicine, Daegu, Korea.

Objectives: The purpose of this retrospective study was to analyze predictive value of pretreatment metabolic tumor volume\r\n(MTV) as determined by F-18 FDG PET/CT for occult LN metastasis (OLM) in invasive ductal breast cancer (IDC).\r\nMethods: A total of forty-one clinically node-negative (cN0) IDC patients (mean age, 50.6±9.5), diagnosed by preoperative\r\nworkups (biopsy, USG, MRI and PET/CT) were enrolled. All patients had undergone surgical resection of primary-tumor\r\nwith sentinel LN biopsy and/or axillary LN dissection without any neoadjuvant treatment. The MTV was defined as the tumor\r\nvolume with more than 75% of the maximum standardized uptake value (SUVmax). Pretreatment variables (age, clinical T\r\nstage, MRI-tumor volume (MRI-TV), SUVmax, and MTV) and posttreatment variables (pathologic T stage, tumor histologic\r\ngrade and lymphovascular invasion) were analyzed to identify their correlation with OLM.\r\nResults: Fourteen (34.1%) of 41 patients were found to have OLM. MTV was significantly higher in patients with OLM\r\n(Negative OLM: 0.82±1.10 vs. Positive OLM: 2.08±2.66, P<0.001). A cutoff of 1.09 ml for the MTV was determined to be the\r\nmost discriminative value for predicting OLM. By univariate analysis, the patients with an MTV of > 1.09 ml had significantly\r\nhigher number of OLM than those with an MTV of ≤ 1.09 ml (P=0.0018). Also, lymphovascular invasion and MRI-TV showed\r\na statistically significant correlation with OLM by univariate analysis (P=0.0303 and 0.0421). Among these three parameters\r\n(MTV, lymphovascular invasion, and MRI-TV), MTV had one of the highest odds ratio associated with the OLM (AUC: 0.730,\r\nodds ratio: 10.667, 95% confidence interval: 2.15–52.85).\r\nConclusion: MTV by F-18 PET/CT demonstrated a significant correlation with OLM in patients with cN0 IDC. Therefore\r\nMTV might be used for LN metastasis predictive factor in patients with cN0 IDC.