Prolonged Responses With Trastuzumab Emtasine Treatment of Human Epidermal Growth Factor Receptor 2-positive Metastatic Breast Cancer Refractory to Trastuzumab and Pertuzumab: Systematic Review of Evidence

Amplification of human epidermal growth factor receptor 2 (HER2) occurs in around 25% of breast cancers and has been associated with aggressive disease. Here, we summarize published evidence on efficacy and prolonged responses with trastuzumab emtansine (T-DM1) after first-line trastuzumab plus pertuzumab and provide possible factors related to prolonged responses to T-DM1. We conducted a literature search using PubMed, and articles that were published in English between July 1, 2012 and December 31, 2019 were included. A review of the bibliography included in the articles found was made. Nine articles were eligible; 2 were case reports, and the remaining 7 were nonexperimental studies, all retrospective. Five were multi-center works. The total number of patients was 796 (276 received pertuzumab). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was used for this systematic review. The population included was heterogeneous among studies according to hormone receptor status, de novo metastatic disease, number of metastatic sites, visceral involvement, brain metastasis, previous neoadjuvant or adjuvant trastuzumab, and line of therapy in which T-DM1 was administered. Less efficacy in terms of responses (overall response rate, 18%-33%) and progression-free survival (4-6 months) with second-line T-DM1, in patients pretreated with pertuzumab, was shown (if compared with the EMILIA trial). The results are more similar to those of the TH3RESA trial (very pretreated population). Prolonged treatments (6 months or more) were observed in at least 17% of cases. The efficacy of T-DM1 after a previous pertuzumab treatment is lower than if pertuzumab is not given, although prolonged responses are observed in this setting.