Supplementary Material for: Neratinib as extended adjuvant treatment of HER2-positive/HR-positive early breast cancer patients in Germany, Austria and Switzerland: interim results of the prospective, observational ELEANOR study

Introduction: Prognosis of patients diagnosed with HER2+ early breast cancer (eBC) has substantially improved, but distant recurrences impacting quality of life and survival still occur. One treatment option for extended adjuvant treatment in patients with HER2+/HR+ eBC is neratinib; available in Europe for patients who completed adjuvant trastuzumab-based therapy within 1 year. The ELEANOR study is investigating the real-world use of neratinib in Germany, Austria and Switzerland. Results from an interim analysis of the first 200 patients observed for ≥3 months are reported. Methods: The primary objective of this prospective, multicentre, observational study is to assess patient adherence to neratinib (defined as percentage of patients taking neratinib on ≥75% prescribed days). Secondary objectives are patient characteristics and treatment outcomes. Results: At cut-off (May 2, 2022), 202 patients had been observed for ≥3 months, with neratinib treatment documented for 187 patients (median age 53.0 years; 67.9% at increased risk of disease recurrence). In total 151 (80.7%) patients had received prior neoadjuvant treatment; of these 82 (54.3%) achieved a pathological complete response. Neratinib was initiated at a median 3.6 months after trastuzumab-based treatment, with 36.4% starting at a dose <240 mg/day. Treatment is ongoing for 46.0% of patients, with median treatment duration of 11.2 (interquartile range 0.9–12.0) months. Diarrhoea was the most common adverse event (78.6% any grade, 20.3% Grade ≥3); pharmacologic prophylaxis was used in 85.6% of patients. Conclusions: The pattern of anti-HER2 pretreatment observed reflected the current treatment for HER2+/HR+ eBC in Germany, Austria and Switzerland. These interim results suggest that neratinib as an extended adjuvant is a feasible option after various anti-HER2 pretreatments, and that its tolerability can be managed and improved with proactive diarrhoea management. ClinicalTrials.gov identifier: NCT04388384