PTGS1 and malignant colon neoplasm: The decreased expression for PLA2G2D and PLA2G5 appears to be linked (cluster II, Figure 5) to that observed for PLA2G4A, ptgs1, SFRP-1 and RLPA-1, which have been proposed as tumour suppressor genes in colon cancer (Chulada et al, 2000; Shida et al, 2004; Suzuki et al, 2004; Dong et al, 2005).