Association Between the Dietary Inflammatory Index (DII) and Head and Neck Cancer Incidence-A Narrative Review.

Head and neck cancer (HNC) comprises a heterogeneous group of tumours, most often of squamous cell origin, characterized by both high morbidity and mortality rates. It is the seventh most common form of cancer diagnosed in humans, accounting for approximately 4.7% of all cancers. Among HNCs, neck squamous cell carcinoma (HNSCC) is predicted to become the most common form of human cancer. Some sources include oesophagus (ESCC) in this group due to their similar histology, being described as upper aerodigestive tract cancers (UADT). Unfortunately, 60-70% of cases are diagnosed late, i.e., at clinical stages III-IV. As a result, despite modern surgical techniques and oncological treatments, the survival rate remains below 40-60% due to frequent lymph node metastases and local tumour recurrence. There is a growing concern that diet and inflammatory dietary components may influence the initiation and development of HNSCC. The inflammatory potential of diets can be quantified by the Dietary Inflammatory Index (DII). The DII was derived from an analysis of 45 dietary constituents that either increase or decrease inflammation. Several recent clinical studies have noted a significant relationship between DII score and many inflammation-associated chronic diseases, such as obesity, cardiovascular and neurodegenerative disorders, and diabetes, and the incidence of various human cancers, i.e., prostate, ovarian, breast, colorectal cancer, and HNC. However, few studies have investigated the relationship between DII and HNSCC, with most being limited to observational, case-control, and cross-sectional studies. Therefore, the aim of this narrative review is to present the substantial oncological aspects of DII, discuss the use of DII and its modification, the Energy-Adjusted Dietary Inflammatory Index (E-DII), as indicators of HNSCC risk. It also introduces key diet-induced pro- and anti-inflammatory mechanisms and the cellular molecular signalling pathways determining the carcinogenesis of HNSCC. It provides a comprehensive overview of the current literature, including key opinion-forming systematic reviews, as well as molecular, observational, cross-sectional and case-control studies, all of which are accessible via scholarly databases such as PubMed/EMBASE/Web of Science. Thus, the work serves as a compendium of up-to-date knowledge on the relationship between DII/ED-II score and HNSCC etiopathogenesis and the influence of a diet-induced persistent inflammatory microenvironment.