In keeping with dominant inhibition of COX-1 activity by aspirin, compared with COX-2, in the CD1 Nude mouse model, intra-tumoral PGE2 levels were reduced only partially by aspirin in both MC38 and MC38r cell tumours (Fig. 5d, e), with an attenuated, statistically insignificant response in MC38r cell tumours, in which COX-2-dependent PGE2 synthesis is increased (Fig. 5d, e). Here, PTGS1 is linked to neoplasm.