Title - The FOXM1-PLK1 axis in oesophageal and gastric adenocarcinoma.Background - Oesophagogastric cancers generally present late in life with advanced disease and carry a poor prognosis. Few patients receive curative treatment. Polo-like Kinase 1 (PLK1) is a mitotic kinase with regulatory functions at the G2/M cell cycle phase transition. In mammalian cells, PLK1 phosphorylates and activates FOXM1, a forkhead transcription factor at the G2/M cell cycle phase transition. FOXM1 then promotes transcription of multiple gene products, including PLK1 and CCNB1, which then act individually or in complexes to further phosphorylate FOXM1 generating a positive feedback loop driving the cell into M phase.Aims - We aimed to assess the expression of PLK1 and FOXM1 in oesophageal and gastric cancer patients. Secondly we aimed to investigate the expression and inter- relationship of PLK1 and FOXM1 in oesophageal cell lines during the cell cycle.Results - FOXM1 and PLK1 are expressed in oesophageal cell lines and demonstrate cross-regulatory interactions. Inhibition of PLK1 leads to the decreased expression of FOXM1 and it's target gene in oesophageal cell lines. FOXM1 and PLK1 are also concomitantly overexpressed in a large proportion of oesophageal and gastric carcinoma's at both the protein and mRNA level. Other FOXM1 target genes including, CCBN1, AURKB and CKS1 are co-expressed in a similar manner. In a homogenous cohort of patients who underwent surgery, the expression of PLK1 and AURKB was prognostic for overall survival.Conclusions - This study has demonstrated that FOXM1 and a number of target genes including PLK1 are coordinately expressed in a proportion of oesophageal and gastric carcinomas. This suggests that chemotherapeutic treatments that target this pathway may be of clinical utility.