Purpose: Our purpose in this study was to assess the added clinical value of hybrid 18F-FDG-PET/MRI compared to conventional imaging for locoregional staging in breast cancer patients undergoing neoadjuvant chemotherapy (NAC).
Methods: In this prospective study, primary invasive cT2-4 N0 or cT1-4 N+ breast cancer patients undergoing NAC were included. A PET/MRI breast protocol was performed before treatment. MR images were evaluated by a breast radiologist, blinded for PET images. PET images were evaluated by a nuclear physician. Afterwards, a combined PET/MRI report was written. PET/MRI staging was compared to conventional imaging, i.e., mammography, ultrasound and MRI. The proportion of patients with a modified treatment plan based on PET/MRI findings was analyzed.
Results: A total of 40 patients was included. PET/MRI was of added clinical value in 20.0% (8/40) of patients, changing the treatment plan in 10% and confirming the malignancy of suspicious lesions on MRI in another 10%. In seven (17.5%) patients radiotherapy fields were extended because of additional or affirmative PET/MRI findings being lymph node metastases (n = 5) and sternal bone metastases (n = 2). In one (2.5%) patient radiotherapy fields were reduced because of fewer lymph node metastases on PET/MRI compared to conventional imaging. Interestingly, all treatment changes were based on differences in number of lymph nodes suspicious for metastasis or number of distant metastasis, whereas differences in intramammary tumor extent were not observed.
Conclusion: Prior to NAC, PET/MRI shows promising results for locoregional staging compared to conventional imaging, changing the treatment plan in 10% of patients and potentially replacing PET/CT or tissue sampling in another 10% of patients.
Keywords: Breast cancer; Locoregional staging; Neoadjuvant chemotherapy; PET/MRI.