Despite the inherent major challenges associated with the development of COX-2 selective radiotracers for PET imaging of COX-2 in vivo, we believe that radiotracer [18F]Pyricoxib based on a pyrimidine scaffold does show the best and most selective tumor uptake profile in COX-2-expressing tumors as analyzed in a pre-clinical in vivo model so far. The gene discussed is PTGS2; the disease is neoplasm.