Our data demonstrating that loss of CT26 CRC cell COX expression has similar effects on the anti-tumour activity of EPA in both immunocompetent BALB/c and immunocompromised CD1 Nude mice contrast with the study of Zelenay et al., in which genetic and pharmacological COX inhibition (in this case using the selective COX-2 inhibitor celecoxib) reduced CT26 cell tumour growth in immunocompetent, but not immunocompromised mice [19]. Here, PTGS2 is linked to colorectal carcinoma.