Abstract 120P
Background
Guidelines recommend adjuvant systemic therapy for stage I HER2+ breast cancer (BC). There might be a risk of undertreatment when neoadjuvant systemic treatment (NST) with paclitaxel and trastuzumab (PT) is given due to potential inaccuracy of clinical staging reflected by 20% of sentinel node positivity in patients undergoing upfront surgery. However, NST provides downstaging and response-guided adjuvant treatment. Here, we investigate the role of PET-CT in clinical staging and the effect of PET-CT and NST on residual breast and nodal disease in clinical stage I HER2+ BC.
Methods
Patients with stage I HER2+ BC (IHC 2+ with ISH amplification or IHC 3+) diagnosed between 2011 – 2020 were selected from a local database. Main exclusion criteria were history of DCIS and/or ipsilateral BC, bilateral HER2+ BC, no sentinel node procedure. Patient reports were reviewed to determine if PET-CT contributed to clinical staging. Pathology reports were reviewed to determine pathological breast and nodal disease.
Results
In total, 182 patients were included of which 127 did not undergo PET-CT. The majority of these patients (110/127, 87%) had upfront surgery with 22 patients (20%) having pN+. The remaining 17 patients were treated with NST, 11 with PT and 6 with a more intense regimen. All 17 patients without PET-CT prior to NST were ypN0. Among 55 patients who underwent PET-CT, in 2 patients (3.6%) PET-CT detected positive axillary lymph nodes, confirmed using FNA. Of the 53 patients with cN0, 52 (98.1%) were treated with NST; 35 received PT and 17 a more intense regimen. Four out of 52 patients (7.7%) had ypN+ after NST, (PT: 3/35, 8,6%, other regimen: 1/17, 5.9%). Out of all the 69 patients treated with NST, 58% had a pCR (PT: 26/46, 57%, other regimen: 14/23, 61%).
Conclusions
PET-CT scan has limited added value for clinical staging in patients with stage I HER2+ BC with only 3.6% having N+ on PET-CT. NST substantially reduced the node-positive rate in patients with clinically stage I HER2+ BC. Given the high pCR rate and small numbers of patients with N+ after NST, PT-regimen in the neoadjuvant setting could be considered. Future studies are needed to assess (de-) escalation strategies for patients with residual disease after neoadjuvant PT.
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
M. Kok: Financial Interests, Institutional, Funding: BMS, Roche, AstraZeneca; Financial Interests, Institutional, Advisory Board: AstraZeneca, Daiichi Sankyo, Domain Therapeutics, Alderaan, BMS, MSD, Roche; Financial Interests, Institutional, Invited Speaker: Roche, BMS, Gilead. All other authors have declared no conflicts of interest.