Review: Merging from traditional to potential novel breast cancer biomarkers

Breast cancer biomarkers are the main player in decision-making in diagnosis, prognosis, and treatment. Estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) are well-known in breast cancer management. Additionally, the Ki-67 protein is used as a tumor proliferation indicator to asses the cancer aggressiveness. Recently, the field has been rapidly integrating novel biomarkers to develop precise, personalized with high effectiveness in patient care. A group of merging biomarkers, including genomic and transcriptomic signatures, circulating tumor cells (CTCs), cell-free DNA (cfDNA), tumor-infiltrating lymphocytes (TILs), and immune checkpoint proteins such as PD-L1, all showed promising toward revealing tumor behavior, treatment response, and potential metastatic spread. microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are merging as new potential diagnostic tools. All mentioned merging innovative biomarkers showed promising results, yet challenges remain in their validation, standardization, and integration into routine clinical practice. This review will highlight the transition from traditional to novel strategies, developing more effective treatments that improve breast cancer patients' outcomes and survival.