Musa Baris Aykan

Abstract The low expression of human epidermal growth factor receptor 2 (HER2) in hormone receptor positive (HR +) metastatic breast cancer has become a novel area of interest, particularly after the demonstration that it can be targeted with antibody–drug conjugates (ADCs).

1 INTRODUCTION Immune checkpoint inhibitors (ICIs) became an indispensable part of the oncology practice for almost all patients with advanced cancers,1 including but not limited to melanoma,2 renal cell carcinoma (RCC),3 non-small cell lung cancer (NSCLC),4 gastric cancer5 and Hodgkin lymphoma (HL).6 Furthermore, the ICIs entered into the adjuvant or neoadjuvant in several tumors.7-9 However, the advances in ICIs were not uniform for all tumors.