PTGS2 and ductal breast carcinoma in situ: It has been proposed that COX-2 expression in ductal carcinoma in situ (DCIS) has a crucial role in the development of breast cancer, with the ability of DCIS to progress to invasive breast cancer being dependent on the COX-2 enzyme's role in the destruction of the basal membrane and in the formation of new blood vessels allowing tumour growth (Imada et al, 2006).