Breast cancer is the most prevalent cancer globally, with 3 million new cases and over 600,000 deaths in 2022. The clinical heterogeneity of breast cancer and challenges in early diagnosis necessitates advanced molecular biomarkers to guide personalized therapy. This research highlights the role of cancer biomarkers? such as hormone receptors (HR), HER2, Ki-67, and PIK3CA mutations in molecular subtyping, prognostication, and targeted treatment. Luminal A, Luminal B, HER2-enriched, triple-negative, and normal-like are among the subtypes of breast cancer that enhance better-targeted treatment plans leading to better outcomes. Additionally, biomarkers help identify resistance mechanisms, which is crucial for tailored treatments. Targeted treatments, including HER2 inhibitors, hormone-based therapies, CDK4/6 inhibitors, and PARP inhibitors, have improved survival rates in patients with specific molecular profiles. To improve the accuracy of diagnosis and treatment, future studies will concentrate on liquid biopsies, multi-omics technologies, and AI-driven biomarker discovery. However, challenges in access to biomarker-based diagnostics and treatments remain, particularly in low- and middle-income countries. This review highlights how cancer biomarkers have revolutionized personalized oncology by providing insights into the course of cancer and opening the door to novel treatment approaches.