Background: Gangliocytic paraganglioma (GP) is an extremely rare benign tumor that commonly arises from the\nsecond part of the duodenum. Since GP exhibit neither prominent mitotic activity nor Ki-67 immunoreactivity, this\ntumor is often misdiagnosed as neuroendocrine tumor (NET) G1 (carcinoid tumor). However, patients with GP may\nhave a better prognosis than patients with NET G1. This fact emphasizes the importance of differentiating GP from NET\nG1, but few studies have reported the epidemiology and histopathology of GP because of its rarity. To differentiate GP\nfrom NET G1 with ease, we conducted a multi-institutional retrospective study analyzing the morphometric and\nimmunohistochemical features of this tumor.\nMethods: Since only a limited number of patients with GP could be identified in our institute, we conducted a\nmulti-institutional retrospective study of GP in Japan, which was approved by the Ethics Committee of our medical\ninstitute. The obtained tissue sections underwent detailed morphometric and immunohistochemical analyses.\nAdditionally, to differentiate GP from NET G1 with ease, immunohistochemical findings were compared.\nResults: In our examination of 12 cases of duodenal GP, we found that epithelioid cells of GP exhibited positive\nreactivity for progesterone receptor and pancreatic polypeptide, whereas tumor cells of NET G1 were completely\nnegative reactivity for both. Additionally, although GP is considered to be an extremely rare NET, we found that\nfour (40.0%) of the ten patients at our institute with duodenal NET G1 actually had GP.\nConclusions: Although GP is regarded as a rare NET, our results suggest that it accounts for a substantial\npercentage of duodenal NETs. Additionally, confirmation of immunoreactivity for progesterone receptor and\npancreatic polypeptide can assist in differentiating GP from NET G1.
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