Can a cup a day keep cancer away? A systematic review exploring the potential of coffee constituents in preventing oral squamous cell carcinoma

Background: Coffee is one of the most consumed beverages in the world. Containing an abundance of bioactive molecules including polyphenols and flavonoids, the constituents of this beverage may exert antiproliferative, antioxidant and anti-inflammatory effects. Methods: We conducted a systematic review to summarise the available evidence on the anticancer effects of coffee constituents and their potential therapeutic use for oral squamous cell carcinoma (OSCC). Studies were identified through a comprehensive search of OVID MEDLINE, OVID EMBASE and Web of Science, including articles from any year up to 15 May 2023. Results: Of the 60 reviewed papers, 45 were in vitro, 1 was in silico and 8 were in vivo exclusively. The remaining studies combined elements of more than one study type. A total of 55 studies demonstrated anti-proliferative effects, whilst 12 studies also investigated migration and invasion of neoplastic cells. The constituents studied most frequently were quercetin and epigallocatechin gallate (EGCG), demonstrating various cytotoxic effects whilst also influencing apoptotic mechanisms in cancer cell lines. Dose-dependent responses were consistently found amongst the studied constituents. Conclusion: Whilst there was heterogeneity of study models and methods, consistent use of specific models such as SCC25 for in vitro studies and golden hamsters for in vivo studies enabled relative comparability. The constituents of coffee have gained significant interest over the last 30 years, particularly in the last decade, and present an area of interest with significant public health implications. Currently, there is a paucity of literature on utilization of active coffee constituents for the therapeutic treatment of oral cancers.