Background: The year 2025 has been transformative in breast oncology, marked by the maturation of pivotal adjuvant trials, the introduction of novel antibody-drug conjugates (ADCs), and the validation of proactive biomarker-driven strategies across all molecular subtypes. The ASCO, ESMO, SABCS contributed pivotal updates that further refined treatment paradigms. Objectives: This systematic review synthesizes and critically evaluates pivotal Phase II/III clinical trials presented at major oncology conferences (ASCO 2025, ESMO 2025, SABCS 2025) and published in high-impact journals during 2025. Methods: A curated selection of pivotal Phase II/III trials, and major prospective trials published or presented in 2025 was performed. Data extraction focused on trial design, population, interventions, efficacy endpoints, and safety outcomes. Narrative synthesis was organized by disease stage and molecular subtype. Results: Key 2025 findings (50 clinical trials) include: (1) confirmation of overall survival benefit with adjuvant CDK4/6 inhibitors in HR+/HER2− early breast cancer (monarchE: HR=0.842, p=0.0273); (2) establishment of trastuzumab deruxtecan (T-DXd) as a new standard in high-risk HER2+ early disease (DESTINY-Breast05: IDFS HR=0.47) and first-line metastatic settings (DESTINY-Breast09: PFS HR=0.58); (3) validation of TROP2-directed ADCs as first-line therapy for metastatic triple-negative breast cancer (ASCENT-03: PFS HR=0.62; BEGONIA: ORR 79%); (4) paradigm shift to proactive, liquid biopsy-guided therapy switching (SERENA-6: PFS HR=0.44); (5) updated efficacy and safety of the oral SERD imlunestrant from the EMBER-3 trial, supporting its role in ESR1-mutated advanced breast cancer and in combination with abemaciclib; (6) confirmation of long-term survival benefit for neoadjuvant carboplatin in early TNBC and new positive adjuvant data; (7) pivotal advances in HER2+ metastatic disease sequencing with tucatinib and T-DXd; and (8) evidence supporting optimized adjuvant endocrine therapy in HER2+/HR+ early disease. and (5) emergence of novel agents with improved therapeutic indices, including PROTAC degraders, oral SERDs, and mutant-selective PI3K inhibitors. Conclusion: The 2025 evidence base has fundamentally reshaped breast cancer management, establishing new standards of care across all subtypes. Unifying themes include biomarker-driven personalization, strategic treatment sequencing, management of unique toxicities, and emphasis on patient-reported outcomes. Future challenges include optimizing treatment integration, managing financial toxicity, and ensuring equitable global access.