Gastric and intestinal phenotypic correlation between exocrine and endocrine components in human stomach tumors

Case of gastric neuroendocrine carcinoma showing an interesting tumorigenic pathway

Here, we report a case of gastric neuroendocrine carcinoma showing an interesting tumorigenic pathway. A 57-year-old Japanese woman presented with epigastric tenderness, and distal gastrectomy was performed. In the surgical specimen, histologically, the tumor tissue was composed of three subtypes of tumor components showing different histological architecture and cellular atypia, diagnosed as neuroendocrine tumor (NET) G2, NET G3, and neuroendocrine carcinoma (NEC) components. Immunohistochemically, the Ki-67-positive rates of NET G2, NET G3, and NEC components were 6.5%, 99.5% and 88.1%, respectively. Although allelic imbalance (AI) on chromosomes 1p, 3p, 8q, TP53, 18q and 22q was commonly found in all components, AI of 4p was found in NET G3 and NEC components (but not in the NET G2 component). In contrast, AIs of 5q and 9p were found in only the NEC component. Thus, we showed the progression from NET G2 to NEC, via NET G3, within the same tumor.

Mucin phenotype expression of gastric neuroendocrine neoplasms: analysis of histopathology and carcinogenesis

BACKGROUND

Gastric neuroendocrine neoplasia has been classified as neuroendocrine tumor (NET), a less-malignant type, and neuroendocrine carcinoma (NEC), a more-malignant type. We investigated phenotypic expression profiles to clarify the differences between NET and NEC in terms of histopathology and carcinogenesis.

METHODS

We assayed 86 cases of gastric neuroendocrine neoplasms (NET G1, n = 25; NET G2, n = 9; NEC, n = 52), using six exocrine markers (MUC5AC, human gastric mucin, MUC6, M-GGMC-1, MUC2, and CDX2).

RESULTS

NEC frequently coexisted with adenocarcinomatous components (75 %; 39 of 52) and the majority (71.8 %; 28 of 39) showed intraglandular endocrine cell hyperplasia, although no cases of NET showed adenocarcinomatous components. Mucin phenotype significantly differed between NET and NEC; none of NET cases expressed any exocrine markers other than CDX2, although the majority of NEC (86.5 %; 45 of 52) expressed at least one or more exocrine markers with various positive rates for each marker (range, 8.2-74.0 %). Each NEC component showed only the phenotype expressed in the adenocarcinomatous component in the same tumor. Furthermore, double immunohistochemistry revealed dual expression of CDX2 and chromogranin A in half the NEC cases (23 of 46).

CONCLUSIONS

These data suggest that gastric NETs (G1 and G2) and NECs have different processes of carcinogenesis, and gastric NECs may be generated from preceding adenocarcinomas.

BCL6 degradation caused by the interaction with the C-terminus of pro-HB-EGF induces cyclin D2 expression in gastric cancers

BCL6 is a transcriptional repressor that has important functions in lymphocyte differentiation and lymphomagenesis, but there have been no reports of BCL6 expression in gastric cancers. In the present study, we investigated the BCL6 function in gastric cancers. Treatment with TPA resulted in BCL6 degradation and cyclin D2 upregulation. This phenomenon was inhibited by the suppression of the nuclear translocation of HB-EGF-CTF (C-terminal fragment of pro-HB-EGF). The HB-EGF-CTF nuclear translocation leads to the interaction of BCL6 with HB-EGF-CTF and the nuclear export of BCL6, and after that BCL6 degradation was mediated by ubiquitin/proteasome pathway. Real-time RT-PCR and siRNA targeting BCL6 revealed that BCL6 suppresses cyclin D2 expression. Our data indicate that BCL6 interacts with nuclear-translocated HB-EGF-CTF and that the nuclear export and degradation of BCL6 induces cyclin D2 upregulation. We performed immunohistochemical analyses of BCL6, HB-EGF and cyclin D2 in human gastric cancers. The inverse correlation between BCL6 and cyclin D2 was also found in HB-EGF-positive human gastric cancers. BCL6 degradation caused by the HB-EGF-CTF also might induce cyclin D2 expression in human gastric cancers. Inhibition of HB-EGF-CTF nuclear translocation and maintenance of BCL6 function are important for the regulation of gastric cancer progression.