<prompt> Most common site for carcinoid tumor isEsophagusLungAppendixIleum  <response>: Carcinoid tumour arise from the enterochromaffin cells Kulchitsky cells found in the crypts of Lieberkuhn. These cells are capable of APUD Amine precursor uptake and Decarboxylation and can secrete vasoactive amines like 5- HT, 5-HIAA, 5-HTP; tachykinins, peptides chromograninsand PGs. It commonly occurs in appendix 45, ileum 25 and rectum 15. Other 15 sites are--other pas of GIT including pancreas and biliary tract, bronchus and testis. Reference: page 877 SRBs manual of surgery 5th edition. 