PACE: A Randomized Phase II Study of Fulvestrant, Palbociclib, and Avelumab After Progression on Cyclin-Dependent Kinase 4/6 Inhibitor and Aromatase Inhibitor for Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor-Negative Metastatic Breast Cancer.

PURPOSE: Cyclin-dependent kinase (CDK) 4/6 inhibitors (CDK4/6is) are an important component of treatment for hormone receptor-positive/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC), but it is not known if patients might derive benefit from continuation of CDK4/6i with endocrine therapy beyond initial tumor progression or if the addition of checkpoint inhibitor therapy has value in this setting. METHODS: The randomized multicenter phase II PACE trial enrolled patients with hormone receptor-positive/HER2- MBC whose disease had progressed on previous CDK4/6i and aromatase inhibitor (AI) therapy. Patients were randomly assigned 1:2:1 to receive fulvestrant (F), fulvestrant plus palbociclib (F + P), or fulvestrant plus palbociclib and avelumab (F + P + A). The primary end point was investigator-assessed progression-free survival (PFS) in patients treated with F versus F + P. RESULTS: Overall, 220 patients were randomly assigned between September 2017 and February 2022. The median age was 57 years (range, 25-83 years). Most patients were postmenopausal (80.9%), and 40% were originally diagnosed with de novo MBC. Palbociclib was the most common previous CDK4/6i (90.9%). The median PFS was 4.8 months on F and 4.6 months on F + P (hazard ratio [HR], 1.11 [90% CI, 0.79 to 1.55]; P = .62). The median PFS on F + P + A was 8.1 months (HR v F, 0.75 [90% CI, 0.50 to 1.12]; P = .23). The difference in PFS with F + P and F + P + A versus F was greater among patients with baseline ESR1 and PIK3CA alterations. CONCLUSION: The addition of palbociclib to fulvestrant did not improve PFS versus fulvestrant alone among patients with hormone receptor-positive/HER2- MBC whose disease had progressed on a previous CDK4/6i plus AI. The increased PFS seen with the addition of avelumab warrants further investigation in this patient population.

Impact of Neoadjuvant Paclitaxel/Trastuzumab/Pertuzumab on Breast Tumor Downsizing for Patients with HER2+ Breast Cancer: Single-Arm Prospective Clinical Trial.

BACKGROUND: The impact of abbreviated neoadjuvant regimens for HER2+ breast cancer on rates of breast conservation therapy (BCT) is unclear. We aimed to determine BCT rates in a single-arm prospective trial of neoadjuvant paclitaxel/trastuzumab/pertuzumab (THP) in patients with stage II or III HER2+ breast cancer. STUDY DESIGN: BCT eligibility was prospectively recorded before and after THP. Pre- and posttreatment mammogram and breast ultrasound were required; breast MRI was encouraged. Patients with a large tumor to breast size ratio were eligible for downsizing. Multifocal/multicentric tumors, extensive calcifications, and contraindications to radiation were considered BCT contraindications. RESULTS: Overall, 92 patients who received neoadjuvant THP on trial were included. At presentation, 39 (42.4%) were considered eligible for BCT and 53 (57.6%) were not. BCT-eligible patients were older (median 54 vs 47 years, respectively; p = 0.006) and had smaller tumors by palpation (median 2.5 vs 3 cm, respectively; p = 0.004). Of 53 BCT-ineligible patients, 28 were candidates for tumor downsizing, whereas 25 had contraindications to BCT. Overall, 51 (55.4%) patients underwent BCT. Of the 28 patients who were candidates for downsizing, 22 (78.6%) became BCT-eligible after THP and 18 of 22 (81.8%) underwent BCT. In total, 44 of 92 (47.8%) patients experienced breast pathologic complete response (ypT0), including 11 of 25 (44.0%) patients with BCT contraindications at presentation. CONCLUSIONS: De-escalated neoadjuvant systemic therapy led to high BCT rates in this cohort. The impact of de-escalated systemic therapy on local therapy and outcomes in early stage HER2+ breast cancer warrants further investigation.

A prospective trial of treatment de-escalation following neoadjuvant paclitaxel/trastuzumab/pertuzumab in HER2-positive breast cancer.

De-escalating adjuvant therapy following pathologic complete response (pCR) to an abbreviated neoadjuvant regimen in human epidermal growth factor receptor 2-positive (HER2+) breast cancer is the focus of international research efforts. However, the feasibility of this approach and its appeal to patients and providers had not been formally investigated. We aimed to assess adherence to de-escalated adjuvant antibody doublet therapy (trastuzumab and pertuzumab [HP], without chemotherapy) among patients with pCR following neoadjuvant paclitaxel/HP (THP). In this single-arm prospective trial, patients with treatment-naïve stage II-III HER2+ breast cancer received neoadjuvant weekly paclitaxel ×12 and HP every 3 weeks ×4. The primary endpoint was receipt of adjuvant non-HER2-directed cytotoxic chemotherapy. Ninety-eight patients received ≥1 dose of THP on study. Patients had median age of 50 years, 86% had stage II tumors, and 34% were hormone receptor-negative. Five patients had incomplete clinical response following THP and received doxorubicin and cyclophosphamide before surgery; they were classified as non-pCR and censored from further analyses. The overall pCR rate was 56.7%. Among patients with pCR, the adherence rate to de-escalated antibody-only therapy (HP) was 98.2% (95% CI 90.3-100.0%), and the primary feasibility endpoint was reached. The majority of patients felt positive or neutral about their adjuvant treatment plans. With brief follow-up (median 19.1 months), there were no breast cancer recurrences. De-escalation of adjuvant chemotherapy among patients who experience pCR in early-stage HER2+ breast cancer is a practicable approach for both patients and physicians. Planned and ongoing prospective trials will determine the long-term efficacy of this approach.Trial registration clinicaltrials.gov, NCT03716180, https://clinicaltrials.gov/ct2/show/NCT03716180 .