Differences in Outcomes Between Human Epidermal Growth Factor Receptor 2 (HER2)-Positive Metastatic Breast Cancer Patients in Upper Middle-Income versus High-Income Countries: A Retrospective Study from 4 Oncology Centers.

BACKGROUND Therapeutic options for human epidermal growth factor 2 (HER2)-positive metastatic breast cancer (mBC) are developing rapidly. This study aimed to determine the differences in the survival outcomes of patients with HER2-positive mBC in relation to access to anti-HER therapy at 3 oncology centers in upper-middle-income countries (UMICs) and 1 oncology center in a high-income country (HIC). MATERIAL AND METHODS We retrospectively identified 42 patients from Croatia (HIC), 71 patients from Serbia (UMIC), and 57 from Bosnia and Herzegovina (UMIC) diagnosed with HER2-positive mBC who were treated between January 2015 and December 2020. The pathohistological features of the tumors were obtained from the pathological findings, which were made according to standard procedures for each center. Patients were treated depending on the availability of therapy, which differed for centers in different countries. We evaluated disease-free survival, progression-free survival, and overall survival (OS) based on the availability of first- and second-line anti-HER2 therapy in UMICs vs HIC. RESULTS OS in first-line therapy was better in patients treated with dual HER2 blockade than in patients treated without dual HER2 blockade, P<0.001. OS in second-line therapy was significantly better in patients treated with trastuzumab emtansine than in patients treated with other reported regimens, P=0.004. CONCLUSIONS Results of our study showed superior survival among patients who were treated with dual first-line HER2 therapy as well as second-line trastuzumab emtansine therapy than in those patients in other centers where these drugs were not available. Raising awareness about this could help improve the situation.