Background Neuroendocrine neoplasms (NENs) can arise in most of the epithelial organs of the body and are not a rare condition in the gastrointestinal tract (GIT). The presence of NENs in GIT associated with other secondary primary malignancies (SPM) has been considered an exotic event. This study aims to describe the case reports of NENs accompanied by synchronous primary tumors. Methods and findings We performed a systematic literature search of the databases Scopus, PubMed, Scielo and LILACS to identify case reports that described the presence of NENs in GIT with SPM. 78 case reports were included. The mean of age of the cases was 60.2 years. 60% were male. 95.4% were NENs G1. 17 cases of NENs had metastasis. 80% of SPM were recognized in the GIT (36% in stomach, 27% in large intestine, 11.2% in small intestine, and 5.6% in esophagus). The most common type of SPM was adenocarcinoma (49.4%), followed by GIST (13.5%), other NENs in different GIT segment (7.9%), lymphoma (6.8%), and squamous cell carcinoma (4.5%). The most common tumor in GIT was adenocarcinoma (97.6%) and the presence of adenocarcinoma in the same segment of GIT was found in 68.4% of the cases. Association between adenocarcinomas and NENs in GIT (p:<0.0001) and adenocarcinoma and tumor in the same segment of GIT location were observed (p<0.001). Conclusion 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.

Background: The presence of a lymphoma associated with a solid synchronous neoplasm or collision neoplasm has been rarely in the literature, and a detailed characterization of these cases is lacking to date.Objective: To describe the main clinicopathological features of synchronous/collision tumors.Methods: A systematic search in PubMed, Scielo, and Virtual Health Library literature databases for cases or case series of synchronous or collision lymphoma and other solid neoplasms reported up to March 2021 was performed. Three reviewers independently screened the literature, extracted data, and assessed the quality of the included studies. The systematic review was performed following the Preferred Reporting Items for Systematic Meta-Analyses guidelines.Results: Mean age of patients was 62.9 years (52.9% men). A total of 308 cases were included (62% synchronous and 38% collision). The most frequent location of both synchronous and collision tumors was the gastrointestinal tract with the most common solid neoplasm being adenocarcinoma, and the most frequent lymphoma diffuse large B-cell lymphoma (21.7%) and mucosa-associated lymphoid tissue lymphoma (20.4%). Of the total number of mucosa-associated lymphoid tissue lymphomas and gastric adenocarcinomas, the presence of Helicobacter pylori infection was documented in 47.3% of them. Only 2% of all cases had a previous history of lymphoma. Thus, in most cases (98%), lymphoma was discovery incidentally. In addition, nodal lymphoma was associated with metastasis in 29 (9.4%) cases as collision tumor, most commonly (90%) in locoregional lymph nodes of the solid neoplasm. Conclusions:The frequent association of some type of B-cell lymphoma and adenocarcinoma in synchronous/collision tumors of the gastrointestinal tract points to common pathogenic mechanisms in both neoplasia, particularly related to chronic inflammation in this location. In most cases, lymphoma identified in locoregional lymph nodes or distant of a carcinoma seems to represent an incidental finding during the carcinoma diagnostic/therapeutic approach. A synergy between carcinoma and lymphoma (involving inflammation and immunosuppression mechanisms) may favor tumor progression and dissemination. A better understating of the interactions lymphoma/carcinoma in the setting of synchronous/collision tumors may help to improve patient management and prognosis.