The run-in phase of the prospective WSG-ADAPT HR+/HER2– trial demonstrates the feasibility of a study design combining static and dynamic biomarker assessments for individualized therapy in early breast cancer

Background: Endocrine sensitivity, as determined by response of the proliferation marker Ki-67 to short-term preoperative endocrine therapy (ET), is currently not included in adjuvant treatment decisions in hormone receptor (HR)+/human epidermal growth factor receptor 2 (HER2)− breast cancer (BC). Methods: The prospective WSG-ADAPT HR+/HER2− trial included patients with N0/N1 early BC who were candidates for adjuvant chemotherapy based on clinical–pathological criteria alone. The trial utilized a genomic assessment [the Recurrence Score (RS)] plus endocrine sensitivity testing to guide treatment. All patients received 3 (±1) weeks of preoperative induction ET. According to protocol, patients with RS 0–11 or RS 12–25 plus endocrine proliferation response (EPR, post-induction Ki-67 ⩽ 10%) were to be spared adjuvant chemotherapy. Results: The ADAPT HR+/HER2− trial run-in phase included 407 patients with baseline RS, of whom 386 (median age: 54 years) had complete data for Ki-67 at both baseline and post-induction. RS distribution: 23.1% RS 0–11, 58.3% RS 12–25, and 18.7% RS 26–100. EPR occurred in 84.3%, 76.0%, and 36.1% of these RS groups, respectively. Differences in EPR proportions (RS 26–100 versus others, RS 0–11 versus others) were significant (both p S = 0.7, n = 181). Conclusions: This phase of the WSG-ADAPT HR+/HER2− trial confirms trial design estimates of RS and EPR. It indicates that the ADAPT concept of combining static and dynamic biomarker assessment for individualized therapy decisions in early BC is feasible using the EPR criterion post-induction Ki-67 ⩽ 10%. Clinicaltrials.gov identifier: NCT01779206.