Abstract
HER-2-positive breast cancer is characterized by its aggressive nature, poor prognosis, and reduced overall survival. The emergence of trastuzumab resistance is currently considered a global problem. The immune system plays a pivotal role in tumor progression and development. Cytotoxic T lymphocyte-associated protein-4 (CTLA-4) and other immune checkpoint proteins may be potential prognostic factors and therapeutic targets for breast cancer. This study aimed to determine the correlation between CTLA-4 expression in peripheral blood and insulin-like growth factor-1 (IGF-1) serum levels and their impact on trastuzumab responsiveness in HER-2-positive patients with breast cancer. CTLA-4 expression was analyzed in peripheral blood cells using quantitative PCR, while IGF-1 serum levels were assessed through electrochemiluminescence assays. There was a significant increase in CTLA-4 expression at cycle 9, which continued to increase until it reached 4.6 at cycle 17. High IGF-1 levels were observed in newly diagnosed HER-2 positive patients before trastuzumab therapy, significantly decreasing post-therapy (p=0.001). Co-targeting HER-2 and IGF-1 receptors may reduce the risk of recurrence and improve outcomes. In addition, targeted CTLA-4 molecules may improve patient survival and prevent recurrence.