The aim of the manuscript is to discuss the influence of plant polyphenols in overcoming multidrug resistance in four types of solid cancers (breast, colorectal, lung and prostate cancer). Effective treatment requires the use of multiple toxic chemotherapeutic drugs with different properties and targets. However, a major cause of cancer treatment failure and metastasis is the development of multidrug resistance. Potential mechanisms of multidrug resistance include increase of drug efflux, drug inactivation, detoxification mechanisms, modification of drug target, inhibition of cell death, involvement of cancer stem cells, dysregulation of miRNAs activity, epigenetic variations, imbalance of DNA damage/repair processes, tumor heterogeneity, tumor microenvironment, epithelial to mesenchymal transition and modulation of reactive oxygen species. Taking into consideration that synthetic multidrug resistance agents have failed to demonstrate significant survival benefits in patients with different types of cancer, recent research have focused on beneficial effects of natural compounds. Several phenolic compounds (flavones, phenolcarboxylic acids, ellagitannins, stilbens, lignans, curcumin, etc.) act as chemopreventive agents due to their antioxidant capacity, inhibition of proliferation, survival, angiogenesis, and metastasis, modulation of immune and inflammatory responses or inactivation of pro-carcinogens. Moreover, preclinical and clinical studies revealed that these compounds prevent multidrug resistance in cancer by modulating different pathways. Additional research is needed regarding the role of phenolic compounds in the prevention of multidrug resistance in different types of cancer.

Currently, the global incidence of head and neck squamous cell carcinoma (HNSCC) continues to increase, with a large proportion of cases being diagnosed at advanced stages. Conventional oncological treatments are often associated with poor quality of life, while the aggressive biological behavior of these tumors results in recurrence in approximately half of treated patients according to current evidence. The need for rapid, targeted diagnosis and personalized treatment has driven research toward the identification of tumor biomarkers with diagnostic, prognostic, and predictive value for treatment response. In this scoping review, we performed a comprehensive literature search to map the available evidence on tumor biomarkers in HNSCC. We identified a wide range of biomarkers, several of which exhibit overlapping roles, and classified them according to their genomic, proteomic, cytokine-related, tumor microenvironment, metabolic, and microbiota-associated characteristics. This scoping review also summarizes the current evidence regarding biomarkers involved in carcinogenesis, treatment response and therapy resistance, while highlighting their current level of clinical applicability. Although only a limited number of biomarkers have currently been implemented in routine clinical practice in head and neck cancers, the studies included in this review identified several promising candidates with the potential to be incorporated into clinical practice following further prospective validation and methodological standardization. Many additional biomarkers are still under investigation, opening new perspectives for future diagnostic and therapeutic targets and supporting the development of personalized multimodal treatment strategies for patients with HNSCC.