Evaluating the accuracy of 18F-FDG PET-MRI scan in detecting regional lymph node disease in high risk breast cancer patients: PETAL study

Background and purpose: Currently, axillary lymph node dissection (ALND) is the only way to accurately stage the axilla in high-risk breast cancer. Despite its accuracy at detecting axillary lymph node (ALN) disease, it is associated with increased morbidity, requires more operative time and is costly. Recently, there has been a paradigm shift towards de-escalation of surgery in the axilla by performing targeted axillary dissection (TAD) in patients with node positive disease who undergo neoadjuvant chemotherapy. The role of PET-MRI in detecting ALN disease in breast cancer has not been fully explored. This study aims to determine the potential benefits of 18F-FDG PET-MRI to improve accuracy of detecting the extent of ALN metastases in high-risk breast cancer. This in return will improve preoperative staging and guide the extent of axillary surgery in women with high-risk breast cancer. Methods: This is a single institution, prospective, single arm non-randomised pilot study. 14 patients with high-risk features (clinical T stage >2, multifocal breast cancer with suspicious nodes) were enrolled in the study and underwent an 18F-FDG PET-MRI before their surgical management of breast cancer, which included ALND (level 1, 2 and 3 of the axilla). Cross-sectional comparison of PET-MRI with histopathological results was performed. Results: 5 out of 14 patients had concordant negative 18F-FDG PET-MRI and histopathology. 4 out of 14 patients had concordant positive 18F-FDG PET-MRI and histopathology. Remaining 5 patients had discordant 18F-FDG PET-MRI results with histopathology, in which all were falsely negative on 18F-FDG PET-MRI. Conclusions: Our pilot study has proven the feasibility of conducting 18F-FDG PET-MRI in the high-risk breast cancer patient population and shown it may have a role in the detection and staging of ALN metastases. We plan to expand this to larger prospective studies to include all neoadjuvant patients and understand the value of this imaging technique in the setting of targeted axillary dissection.