Background & Aims Small intestinal carcinoids are rare and difficult to diagnose and patients often present with advanced, incurable disease. Although the disease occurs sporadically, there have been reports of family clusters. Hereditary small intestinal carcinoid has not been recognized and genetic factors have not been identified. We performed a genetic analysis of families with small intestinal carcinoids to establish a hereditary basis and find genes that might cause this cancer. Methods We performed a prospective study of 33 families with at least 2 cases of small intestinal carcinoids. Affected members were characterized clinically and asymptomatic relatives were screened and underwent exploratory laparotomy for suspected tumors. Disease-associated mutations were sought using linkage analysis, whole-exome sequencing, and copy number analyses of germline and tumor DNA collected from members of a single large family. We assessed expression of mutant protein, protein activity, and regulation of apoptosis and senescence in lymphoblasts derived from the cases. Results Familial and sporadic carcinoids are clinically indistinguishable except for the multiple synchronous primary tumors observed in most familial cases. Nearly 34% of asymptomatic relatives older than 50 y were found to have occult tumors; the tumors were cleared surgically from 91% of these individuals (21/23). Linkage analysis and whole-exome sequencing identified a germline 4 bp deletion in the gene inositol polyphosphate multikinase (IPMK) that truncates the protein. This mutation was detected in all 11 individuals with small intestinal carcinoids and 17/35 family members whose carcinoid status was unknown. Mutant IPMK had reduced kinase activity and nuclear localization, compared with the full-length protein. This reduced activation of p53 and increased cell survival. Conclusions We found that small intestinal carcinoids can occur as an inherited autosomal dominant disease. The familial form is characterized by multiple synchronous primary tumors, which might account for 22%–35% of cases previously considered sporadic. Relatives of patients with familial carcinoids should be screened to detect curable early-stage disease. IPMK haplo-insufficiency promotes carcinoid tumorigenesis.

Background & Aims Small intestinal neuroendocrine tumors (SI-NET) are serotonin-secreting well-differentiated neuroendocrine tumors believed to originate from enterochromaffin (EC) cells. Intestinal stem cell (ISC) are believed to contribute to formation of SI-NET, although little is known about tumor formation or development. We investigated the relationship between EC cells, ISCs, and SI-NETs. Methods We analyzed jejuno-ileal tissue specimens from 14 patients with familial SI-NETs enrolled in the Natural History of Familial Carcinoid Tumor study at the National institutes of Health from January 2009 to December 2014. Frozen and paraffin-embedded tumor tissues of different stages and isolated crypts were analyzed by in situ hybridization and immunohistochemistry. Tumor clonality was assessed by analyses of mitochondrial DNA. Results We identified multifocal aberrant crypt-containing endocrine cell clusters (ACEC) that contain crypt EC cell micro-tumors in patients with familial SI-NET. RNA in situ hybridization revealed expression of the EC cell and reserve stem cell genes TPH1, BMI1, HOPX, and LGR5low, in the ACECs and more advanced extra-epithelial tumor nests. This expression pattern resembled that of reserve EC cells that express ISC genes; most reside at the +4 position in normal crypts. The presence of multifocal ACECs from separate tumors and in the macroscopic tumor-free mucosa indicated widespread, independent, multifocal tumorigenesis. Analyses of mitochondrial DNA confirmed the independent origin of the ACECs. Conclusion Familial SI-NETs originate from a subset of EC cells (reserve EC cells that express ISC genes) via multifocal and polyclonal processes. Increasing our understanding of the role of these reserve EC cells in the genesis of multifocal SI-NETs could improve diagnostic and therapeutic strategies for this otherwise intractable disease.

Background The aim of this study was to prospectively screen patients with a positive family history of carcinoid small intestine neuroendocrine tumors (SI-NETs) to elucidate the benefits of early detection and operative intervention. Methods A single-center, prospective trial was conducted from 2008 to 2014 that evaluated patients with 2 or more blood relatives with carcinoid SI-NETs. All eligible patients were screened with urine/serum biochemistries and various imaging modalities. Operative intervention was elected in patients found to have at least 1 positive diagnostic study. Results Twenty-nine patients from 13 families had occult carcinoid SI-NETs (15 female, 14 male). Twenty-four of the 29 patients (83%) had multifocal disease found in either the distal jejunum or ileum. On average, 75.9 cm (range, 13–195) of bowel was resected in 1 segment. Three patients were found to have stage IV disease at operation. All stage I-IIIB patients who had R0 resections have remained disease-free, with a median follow-up of 35 months. Conclusion Familial carcinoid SI-NETs often are asymptomatic and can be diagnosed with aggressive screening. With early detection, there may be a window of opportunity for operative resection to change the natural history of this disease and even prove to be curative.