HTR5A and carcinoid tumor: In terms of the involvement of 5-HT in bronchial carcinoids, SFN can be an appropriate agent for carcinoid therapy as it has been reported to reduce the expression of 5-HT receptors including 5-HT2, 5-HT3 and serotonin transporter (SERT) as well as to affect the release of 5-HT in Caco-2 cells [31].