A Pilot Study of Early PET and Biomarker Dynamics in Patients with Stage 2 and 3 Triple Negative Breast Cancer Treated with Neoadjuvant Response-Adapted Chemotherapy with Pembrolizumab (Neoadapt).

TPS624 Background: In patients with triple negative breast cancer (TNBC) the addition of pembrolizumab to neoadjuvant chemotherapy has improved pathologic complete response rates (pCR) and 5-year event free survival (EFS). Patients with TNBC who achieve a pCR have a significantly lower risk of recurrence compared to those with residual disease (RD). However, pCR can only be assessed at the time of surgery after completion of 6 months of intensive chemo-immunotherapy, associated with up to 77% high-grade treatment-related toxicity. Identifying pCR early on is imperative in developing optimized and individualized treatments, however, there are no predictive biomarkers. Studies in HER2-positive breast cancer have shown that early fluorodeoxyglucose positron emission tomography (FDG-PET) changes soon after initiation of neoadjuvant treatment can help predict the pathological outcomes at the time of surgery and also the risk of recurrence. Emerging data also support that clearance of circulating tumor DNA (ctDNA) during neoadjuvant treatment may be associated with higher rates of pCR. We thus designed a study to determine the association of early FDG-PET changes and ctDNA clearance with pCR in early-stage TNBC. Methods: NeoADAPT is a phase 2, open label, single center clinical trial including adult patients with previously untreated clinical stage 2 or 3 TNBC. Participants will receive 4 cycles of neoadjuvant paclitaxel/carboplatin with pembrolizumab (TC/pembro), per standard-of-care (SOC). An FDG-PET will be performed at baseline and after 1 cycle. A breast MRI will be performed at baseline and after completion of 4 cycles of treatment. Patients with a complete clinical response (cCR) will proceed to surgery and will forgo more neoadjuvant treatment. Patients with clinical RD on MRI will complete SOC neoadjuvant therapy with 4 cycles of doxorubicin/cyclophosphamide (AC) with pembro prior to surgery. If RD is identified after surgery, adjuvant therapy will be determined by the treating oncologist, which may include pembro with AC (if not given prior), capecitabine, etc. The primary objective is to evaluate if lack of decrease in maximum FDG-PET standard uptake value of lean body mass (SULmax) by less than 40% after 1 cycle of neoadjuvant treatment correlates with RD at the time of surgery (i.e. determining the negative predictive value of FDG-PET). Additional key endpoints include ctDNA clearance, evaluation of pCR and cCR rates in the treatment population and EFS. Distributions of percent reduction in SULmax will be compared between pCR and no-pCR groups using the Wilcoxon rank sum test. Receiver operating characteristic (ROC) curve analysis will be performed to estimate the ability of FDG-PET SULmax reduction and cCR by MRI in predicting pCR at surgery. Clinical trial information: NCT06245889 .