PTGS2 and adenocarcinoma: More recently, Shimizu K et al. investigated the association of PGE-MUM with clinical characteristics including cancer stage; however, these authors could not show any association between PGE-MUM levels and clinical characteristics, possibly because of the small sample size (total of 21 patients), tumor heterogeneity (adenocarcinoma: 18, squamous cell carcinoma: 3), and low COX-2 expression in the studied group (high expression: 7, low expression: 14) [23].