Although initial studies with fevipiprant, an oral antagonist of chemoattractant receptor-homologous molecule on T-helper type-2 cells (CRTH2) serving as a receptor of prostaglandin D2, showed promising efficacy in patients with allergic asthma [241], the phase 3 studies failed to confirm clinical effectiveness in asthma [242] or CRSwNP and concomitant asthma [243]. Here, PTGDR2 is linked to asthma.