Molecular Profiling and Targeted Therapeutic Strategies in Breast Cancer: Clinical Integration of HER2, CDK4/6, and PI3K Inhibition with Trastuzumab, Abemaciclib and Alpelisib

Advances in molecular oncology have reshaped the management of breast cancer through the development of pathway-specific targeted therapies. In particular, inhibition of HER2, CDK4/6, and PI3K signaling has yielded substantial clinical benefits in molecularly defined patient populations. This review provides an integrated analysis of three representative agents—trastuzumab, abemaciclib, and alpelisib—highlighting their distinct mechanisms of action, clinical efficacy, and translational relevance in breast cancer, with contextual insights into gynecologic oncology. Evidence from pivotal clinical trials and emerging translational studies demonstrates that trastuzumab remains a cornerstone of HER2-positive breast cancer treatment, while also showing activity in HER2-amplified gynecologic malignancies. Abemaciclib, a selective CDK4/6 inhibitor, has significantly improved outcomes in hormone receptor–positive breast cancer and is being actively explored in tumors characterized by cell cycle dysregulation, including endometrial and ovarian cancers. Alpelisib, targeting the PI3Kα isoform, provides meaningful benefit in PIK3CA-mutated breast cancer and represents a promising strategy in gynecologic tumors with aberrant PI3K/AKT/mTOR pathway activation. Collectively, these agents exemplify precision oncology approaches that align therapeutic strategies with tumor biology. Their integration into biomarker-driven, multimodal treatment frameworks underscores a paradigm shift toward personalized cancer care across breast and gynecologic malignancies. Particular emphasis is placed on the translation of molecular diagnostics into clinical decision-making, including patient selection, resistance mechanisms, and sequencing strategies within evolving precision oncology frameworks. Ongoing clinical and translational research will be critical to refine combination strategies, overcome resistance mechanisms, and identify predictive biomarkers to further optimize patient outcomes.