BEYOND TUMOUR VISIBILITY: A BIOMARKER-DRIVEN PHARMACOLOGICAL REVIEW OF CUTANEOUS, ORAL CAVITY AND BREAST MALIGNANCIES

Cancer pharmacotherapy is increasingly guided by molecular characteristics that distinguish biologically heterogeneous tumours and predict their susceptibility to specific interventions. Externally accessible malignancies, including cutaneous melanoma, keratinocyte carcinomas, oral squamous cell carcinoma and breast cancer, offer opportunities for clinical inspection, tissue sampling and longitudinal assessment; however, accessibility does not establish tumour biology or predict therapeutic response. This narrative review examines the molecular pathogenesis, pharmacological vulnerabilities and clinical applications of biomarkers across these malignancies. Evidence was synthesised conceptually from established clinical guidelines, peer-reviewed studies and authoritative oncology resources, with emphasis on clinically actionable biomarkers and recognised limitations of emerging assays. BRAF alterations inform targeted treatment selection in melanoma, while Hedgehog pathway dysregulation provides a therapeutic rationale for selected advanced basal cell carcinomas. In breast cancer, oestrogen and progesterone receptors, HER2, PIK3CA and BRCA1/2 alterations inform distinct endocrine, targeted and DNA repair-directed strategies. PD-L1 assessment contributes to treatment selection in defined head and neck and breast cancer settings. The review also evaluates pharmacokinetic and pharmacodynamic principles, immune-mediated toxicity, acquired resistance, intratumour heterogeneity and circulating tumour DNA. A central finding is that biomarker utility depends on assay validity, tumour context and demonstrated clinical benefit rather than the mere detection of a molecular alteration. Integrating histopathology, validated molecular diagnostics, pharmacological assessment and patient-centred decision-making offers a rational foundation for precision oncology. Future advances require prospective validation, equitable diagnostic access and evidence that biomarker-guided interventions improve survival, treatment tolerability or quality of life.