Mesenteric tumour deposits arising from small‐intestine neuroendocrine tumours are frequently associated with fibrosis and IgG4‐expressing plasma cells

摘要

Aims Mesenteric tumour deposits frequently occur in small‐intestine neuroendocrine tumours. In many instances, these mesenteric tumour deposits are surrounded by a dense fibrotic stroma and have associated lymphoplasmacytic inflammation. The aim of this study was to examine whether mesenteric tumour deposits in patients with small‐intestine NET s neuroendocrine tumours show histological and immunophenotypic overlap with IgG4‐related sclerosing mesenteritis. Methods and results Sixty‐six mesenteric tumour deposits from 66 patients with small‐intestine neuroendocrine tumours with blocks available for further studies were identified from our archives. Cases were assessed for clinicopathological features and the presence of IgG4‐positive and IgG‐positive plasma cells by immunohistochemistry. Ratios of IgG4‐positive to IgG‐positive plasma cells were calculated. Seventeen mesenteric tumour deposits (26%) showed 40 IgG4‐positive plasma cells per high‐power field, and the majority of cases (68%) showed at least some staining of IgG4‐positive plasma cells. Mesenteric tumour deposits with 20 IgG4‐positive plasma cells per high‐power field tended to be larger (25.9?±?13.0 mm versus 18.6?±?15.8?mm; P ?=?0.07), and had more IgG‐positive plasma cells (88?±?24 versus 36?±?37; P ??0.01) and a higher IgG4‐positive/IgG‐positive plasma cell ratio (0.66?±?0.18 versus 0.17?±?0.25; P ??0.01). All but one mesenteric tumour deposit with 20 IgG4‐positve plasma cells had a ratio of 40%. Conclusions IgG4 expression is frequent in mesenteric tumour deposits from small‐intestine neuroendocrine tumours. Undersampling of tumour on biopsies of mesenteric tumour deposits could potentially cause diagnostic confusion with IgG4‐related sclerosing mesenteritis.