Neuroendocrine neoplasms of gastrointestinal tract and secondary primary synchronous tumors: A systematic review of case reports. Casualty or causality?

These results demonstrate that NENs with SPM are not a rare condition. Several theories have been proposed to explain this association; one of these is the ability of NENs to generate synchronous tumors by autocrine and paracrine effect. We observed an association between adenocarcinomas and NENs in the same segment of GIT.