HER2 TREAT Study: Retrospective Study to Estimate the Prevalence of HER2-low in Unresectable and/or Metastatic Breast Cancer Patients Who Progress on Anti-Cancer Therapy Identified as HER2-Negative From Patient Medical Records in The Gulf Cooperation Council

HER2-low Breast cancer (BC) has emerged as a new subtype of BC with distinct clinical, pathological, and prognostic features. Little is known about the prevalence of the HER2-low subtype in HER2-negative patients, and previous reports showed variations in the criteria used to define the HER2-low subtype. Besides, data on the clinical features and prognosis of HER2-low patients are limited, and it is still unclear whether HER2-low BC has a prognostic value. Identifying the prevalence and clinical features of HER2-low BC can help establish a more accurate and reproducible definition of HER2-low BC. In the Gulf Cooperation Council (GCC) region, BC is the most common malignancy in women and still poses a significant burden on healthcare resource utilization, moreover, there is only one record for reimbursed HER2 IHC status, categorized as HER2-positive and HER2-negative. It is important to understand the prevalence, clinical features, and outcomes of HER2-low in BC patients from the GCC In this retrospective, non-interventional, multicenter study, the aim to describe the prevalence of HER2-low BC among the current HER2-negative BC population using rescored HER2 IHC samples. The local treatment patterns and the outcomes will be analyzed using the information abstracted from the corresponding medical chart review. The study will cover the GCC region countries (United Arab Emirates [UAE], Saudi Arabia, Qatar, Kuwait, and Oman)