Introduction: Over time the surgical treatment of axilla in breast cancer has evolved towards a
progressive de-escalation. Considering its gradual switch from a therapeutic to a staging procedure,
the role of preoperative imaging has strongly increased. To date, an unmet need is to achieve the most
accurate assessment of the axilla in order to choose the less invasive surgical treatment. PET/MR is
a new imaging tool with promising results on axillary staging.
The study hypothesis is that PET/MR might provide a single, one-stage, non-invasive, operatorindependent
imaging modality allowing surgeons to select the proper axillary treatment in two
different settings of primary surgery for node-negative breast cancer and primary systemic therapy
(PST) for node-positive breast tumors.
Patients and methods: This study was a prospective comparative study that was carried out at San
Raffaele Hospital and planned in two separate groups:
• N0 group: patients with node negative early (c/iT<3cm) breast cancer who were candidates to
sentinel node biopsy (SNB) and were enrolled to perform an additional PET/MR before surgery.
• N+ group: patients with node positive breast cancer undergoing PST who were recruited to
perform two PET/MR exams, one before and one after PST.
Primary outcome was to compare the staging power between PET/MR vs SNB or axillary dissection
in detecting axillary node macro-metastases (>2 mm), evaluating the concordance rate between the
two tools.
Secondary outcome was to compare PET/MR and Ax-US, evaluating the concordance rate between
the two exams.
Results: From October 2019 to November 2020 forty-eight patients were recruited and analyzed.
• N0 group: 17 patients were analyzed. Mean age was 54.3±11.2 years. All patients had a unifocal
luminal cT1-2 breast cancer. After PET/MR twenty new findings were discovered, 20% being
false positive. PET/MR concordance rate with SNB was 82.4 %. PET/MR and Ax-US were
concordant in 88.2% of cases.
• N+ group: 14 patients were analyzed. Mean age was 47.9±14.1 years. Most of them had a cT2-
3(78.6%), triple negative or Her2-ve (64.3%) breast cancer at diagnosis. After initial PET/MR
twenty-one new findings were discovered, 9.5 % being false positive. PET/MR concordance rate
with SNB was 71.5 %. Preoperative PET/MR and Ax-US were concordant in 92.9% of cases.
Conclusions: To date, current evidence are too preliminary to draw meaningful conclusions on the
role of PET/MR in breast cancer treatment but results from ongoing prospective trials are awaited in
three years and should help decide the potential applications of this cutting-edge imaging tool in
breast cancer patients
