This study focuses on survival extrapolation in HER2-positive breast cancer patients, a subgroup of interest following the introduction of targeted therapies such as trastuzumab.17 HER2 overexpression not only serves as a prognostic marker but has also become crucial for determining the suitability of anti-HER2 therapies,18,19 making it essential to study the impact of extrapolation methods. The gene discussed is ERBB2; the disease is breast cancer.