Essential Oils as a Source of Anticancer Molecules: Critical Assessment of Current Evidence and Methodological Limitations—A Systematic Review

Essential oils (EOs) and their bioactive constituents have attracted growing interest as potential anticancer agents because they can target multiple pathways involved in tumor progression. However, the literature on their anticancer activity is highly heterogeneous and often limited by methodological weaknesses that reduce the reliability and translational value of the reported findings. This systematic review critically assessed the anticancer activity of EOs and EO-derived compounds by considering only studies that met defined methodological criteria. A PubMed search identified 872 articles published between 2015 and 2026, of which 97 were retained after screening based on EO chemical characterization, evaluation of cancer selectivity using non-tumoral control cells, and direct assessment of EO-driven anticancer effects. Across different tumor models, EOs and their constituents consistently showed selective cytotoxic or antiproliferative activity, commonly associated with oxidative stress, mitochondrial dysfunction, apoptosis, cell-cycle arrest, and modulation of oncogenic pathways. Some studies also reported reduced migration, invasion, and tumor-promoting signaling, while nanoformulation improved stability and efficacy in selected models. Overall, despite encouraging preclinical evidence, the translational potential of EO-based anticancer strategies remains limited by recurrent methodological shortcomings and insufficient in vivo validation. Standardized experimental criteria will be essential to improve reproducibility and support future clinical development.