HER2 Amplification Level Predicts Pathological Complete Response in the Neoadjuvant Setting of HER2-Overexpressing Breast Cancer: A Meta-Analysis and Systematic Review

Anti-HER2 therapies have dramatically improved the prognosis of human epidermal growth factor receptor 2 (HER2)-overexpressing cancers. However, the correlation between the HER2 copy number and the response rate to anti-HER2 remains unclear. Here, following the PRISMA method, we performed a meta-analysis in the neoadjuvant setting in breast cancer to study the association between the HER2 amplification level and the pathological complete response (pCR) to anti-HER2 therapies. Nine articles (four clinical trials, five observational studies) were retrieved after full-text screening, involving 11,238 women with locally advanced breast cancer in the neoadjuvant setting. The median HER2/CEP17 ratio cut-off value was 5.0 ± 5.0 (min-max = 1.0-14.0). For the overall population, the median pCR rate was 48% using the random effect model. The studies were categorized in quartiles as follows: ≤2 (Class 1); 2.1 to 5.0 (Class 2); 5.1 to 7.0 (Class 3); and >7.0 (Class 4). After grouping, the pCR rates were 33%, 49%, 57%, and 79%, respectively. When we excluded the study by Greenwell et al., which accounted for 90% of the patients, using the same quartiles, we still observed an increasing rate of pCR as the HER2/CEP17 ratio increased. This is the first meta-analysis demonstrating the relationship between the HER2 amplification level and the percentage of pCR in the neoadjuvant setting among women with HER2-overexpressing breast cancer, with potential therapeutic applications.