Accurate histological terminology for small intestine carcinoid tumors

Abstract

The recent WHO Classification of Tumours of the Digestive System reflects the views of a Working Group that convened for an Editorial and Consensus Conference at the International Agency for Research on Cancer (IARC), Lyon, 10 December 2009 [1]. In this classification, the “neuroendocrine neoplasms of the small intestine” include neuroendocrine tumor (NET), neuroendocrine carcinoma (NEC), mixed adenoneuroendocrine carcinoma, EC cell, serotonin-producing NET, gangliocytic paraganglioma, gastrinoma, L cell, glucagon-like peptide-producing, PP/PYY-producing NETs, and somostatin-producing NET. “Carcinoid tumor” is the generic term traditionally applied to low-grade malignant neoplasms originating from the diffuse endocrine system exclusive of the pancreas and the thyroid C-cell, a term being progressively replaced by “well-differentiated (neuro)endocrine tumors/carcinomas”. It is now acknowledged that they represent a group of related neoplasms, not single pathologic entity. In the WHO classification, the NET includes NET G1 and NET G2, and the term “carcinoid” is used as a synonym of NET G1. We believed that the term “carcinoid tumor” is generic; consequently, the term should be avoided. We have read with great interest the paper by Lee et al. – “Multiple carcinoid tumor of the small intestine preoperatively diagnosed by double-balloon endoscopy” [2]. In the paper, Lee et al. wrote: “Histologic examination of the biopsy sample obtained by endoscopy confirmed the diagnosis of a carcinoid tumor. The tumor was composed of small uniform epithelial cells, which stained positively for chromogranin A and synaptophysin.” We believe that the histological diagnosis of carcinoid tumor is not correct. The description is typical of NET G1, according to the new WHO classification. The authors wrote: “These small tumors were diagnosed as carcinoid tumors by endoscopic findings, whereas histologic examination could not make this diagnosis… Microscopically, the tumors were composed of small uniform epithelial cells which stained positively for chromogranin A and synaptophysin. Furthermore, the largest tumor had invaded the muscularis propria. MIB-1 index was less than 1%.” It is evident that histological diagnosis was not reported. In conclusion, accurate histological diagnosis is necessary for the evaluation of treatment impact in the management of neuroendocrine tumors of the small intestine.