Assessing F-18 FDG uptake in the sentinel lymph node in breast cancer.

Objective: Fluorine-18 fluorodeoxyglucose (18 F-FDG) positron emission tomography/computed tomography (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 re-evaluated 18 F-FDG PET/CT images after locating SLN(s) on PET/CT with the help of SLN single photon emission computed tomography/computed tomography (SPECT/CT) images and assessed 18 F-FDG uptake particularly in the SLN(s). Our goal was to understand if combined evaluation of 18 F-FDG PET/CT and SLN SPECT/CT could be a useful technique for detecting early lymph node metastasis in the axilla. Patients and Methods: 18 F-FDG PET/CT images of newly diagnosed breast cancer patients who also had SLN scintigraphy (SPECT/CT) and biopsy result were analyzed to assess 18 F-FDG uptake in the SLN(s). SLN(s) seen on SPECT/CT images were located on PET/CT images and its metabolic activity was assessed both visually and semiquantitaively using maximum standardized uptake value (SUVmax ). 18 F-FDG PET results were compared with histopathology result of SLN(s). Results: Twenty (20) patients among 130 met the inclusion criteria. SLN SPECT/CT images were very helpful for locating the SLN on 18 F-FDG PET/CT images in all 20 patients. Histopathological analysis of SLN(s) demonstrated metastasis in 7 patients and no metastasis in 13. There was mild (visible) 18 F-FDG uptake in the SLN(s) (SUVmax ranging from 1.2 to 4.1 and metastatic deposit size ranging from 6 to 8 mm) in 6 of 7 patients with SLN metastasis (85.7%). There was no or only faint 18 F-FDG uptake in the SLN(s) (SUVmax less than 1) in 9 of 13 patients with no SLN metastasis (69.2%). ROC analysis indicated that cut-off point of SUVmax was 0.85 for differentiating SLN positive and SLN negative cases (sensitivity: 85.7% and specificity: 61.5 %, area under the curve: 0.747, P < 0.05). Conclusion: Combined evaluation of 18 F-FDG PET/CT and SLN SPECT/CT images to assess 18 F-FDG uptake particularly in the SLN(s) is a new image analysis technique to detect early metastatic disease in the axillary lymph nodes in breast cancer. Although, this technique does not seem to be feasible to use in routine practice mainly due to limitations of current PET/CT technology in detecting small amount of tumor, it is an interesting image analysis technique to know for possible future use.