Implication of ¹⁸F-Fluorodeoxyglucose Uptake of Affected Axillary Lymph Nodes in Cases with Breast Cancer

In order to evaluate affected axillary lymph nodes in breast cancer by positron-emission tomography using (18)F-fluorodeoxyglucose (FDG-PET), an understanding of FDG avidity is important. In the present study, we examined whether certain factors, including lymphatic spread and size of metastatic lymph nodes, were associated with FDG avidity in order to evaluate the benefits of a FDG-PET assessment of axillary node metastases. We retrospectively investigated the cases of 179 consecutive patients with primary breast cancer who underwent FDG-PET preoperatively. Among the 179 patients, 48 (26.8%) had axillary lymph node metastases. The sensitivity, specificity, overall accuracy, and false-negative rates in the diagnosis of axillary lymph node status by FDG-PET were 47.9%, 98.5%, 84.9%, and 52.1%, respectively. The 48 cases with lymph node metastases were divided into two groups based on the presence or not of FDG uptake in the axillary lesions. Clinicopathological features of the primary tumor, including tumor size, standardized uptake value (SUVmax and biomarkers, were not statistically significant factors; only the clinicopathological features of metastatic lymph nodes, including the size of node metastasis, were significantly associated with FDG uptake in the axillary lymph nodes. Among the eight cases of micrometastasis, seven were not detected by FDG-PET. The number of cases with only one affected node was significantly higher in the group without FDG uptake in the axillary lesion. Although the number of lymph node metastases was relatively higher in the FDG-PET-positive patients, the difference was not statistically significant. FDG-PET may help identify patients with high axillary lymph node burden. Our findings imply that preoperative FDG-PET evaluation of lymph nodes is not sufficient to predict lymphatic spread or micrometastasis because FDG avidity is mainly influenced by the size of the tumor.