Alterations in Breast Cancer Biomarkers Following Neoadjuvant Therapy.

Introduction Biomarker changes in patients with residual disease (RD) after neoadjuvant systemic therapy (NAT) have unclear consequences. This study examined the prevalence of biomarker [hormone receptor (HR) and HER2] change and its effect on disease-free survival (DFS) and overall survival (OS). Patients and methods A total of 303 patients treated with NAT from 2008 to 2016 were identified from a prospective database. Biomarker status at diagnosis was determined and retested after NAT in patients with RD. DFS and OS were compared among three groups: no biomarker change, clinically insignificant change in either ER or PR without alteration in HR status, and clinically significant change in at least one biomarker with resultant change in HR or HER2 status. Subgroups with no change and HR change were examined [HR+HER2- no change, triple negative (TN) no change, HR+HER2- to TN, TN to HR+HER2]. Results Overall, 61.4% of patients had RD. Of these, 32.8% had changes in at least one biomarker. At median follow up of 5.48 years, no biomarker change was associated with improved DFS compared with changes in HR or HER2 status (p = 0.043). In addition, no biomarker change (p = 0.005) and clinically insignificant changes in biomarker status (p = 0.019) were associated with improved OS compared with clinically significant changes in HR or HER2 status. Among subgroups, HR+HER2- to TN was associated with worse DFS (p = 0.029) and OS (p = 0.008) compared with HR+HER2- no change. Conclusions Among those with RD, biomarker status change was common and impacted survival in subgroups of HR+ or TN disease. Retesting biomarkers after NAT has prognostic implications.