Assessing ¹⁸F-FDG Uptake in the Sentinel Lymph Node in Breast Cancer

¹⁸F-FDG PET/CT has limited value in early breast cancer. Sentinel lymph node (SLN) biopsy is the current procedure of choice to search for small metastatic deposits in the axillary lymph nodes in early breast cancer. In this retrospective study, we reevaluated ¹⁸F-FDG PET/CT images after locating the SLN on PET/CT with the help of SLN SPECT/CT images and assessed ¹⁸F-FDG uptake, particularly in the SLN. Our goal was to understand if combined evaluation of ¹⁸F-FDG PET/CT and SLN SPECT/CT could be useful for detecting early lymph node metastasis in the axilla. Methods: ¹⁸F-FDG PET/CT images of newly diagnosed breast cancer patients who also had SLN scintigraphy (SPECT/CT) and biopsy results were analyzed to assess ¹⁸F-FDG uptake in the SLN. The SLN seen on SPECT/CT images was located on PET/CT images, and its metabolic activity was assessed both visually and semiquantitatively using SUV_max ¹⁸F-FDG PET results were compared with the histopathology result for the SLN. Results: Twenty patients among 130 met the inclusion criteria. SLN SPECT/CT images were helpful for locating the SLN on ¹⁸F-FDG PET/CT images in all 20 patients. Histopathologic analysis of the SLNs demonstrated metastasis in 7 patients and no metastasis in 13. There was mild (visible) ¹⁸F-FDG uptake in the SLN (SUV_max, 1.2-4.1; metastatic deposit size, 6-8 mm) in 6 of 7 patients with SLN metastasis (85.7%). There was no or only faint ¹⁸F-FDG uptake in the SLN (SUV_max < 1) in 9 of 13 patients with no SLN metastasis (69.2%). Receiver-operating-characteristic curve analysis indicated that the SUV_max cutoff for differentiating SLN-positive from -negative cases was 0.85 (sensitivity, 85.7%; specificity, 61.5%; area under the curve, 0.747; P < 0.05). Conclusion: Combined evaluation of ¹⁸F-FDG PET/CT and SPECT/CT images to assess ¹⁸F-FDG uptake, particularly in the SLN, is a new image analysis technique to detect early metastatic disease in the axillary lymph nodes in breast cancer. Although this technique does not currently seem feasible for use in routine practice, mainly because of the limitations of current PET/CT technology in detecting small tumors, it is an interesting image analysis technique to be aware of for possible future use.