Objective:To investigate the clinicopathological features, diagnosis, genetic alterations, and biological behaviors of hamartomatous inverted hyperplastic polyp (HIHP) in the gastrointestinal tract.Methods:The clinical, sonographic, endoscopic and pathologic data of 10 HIHP cases diagnosed at the First Affiliated Hospital of Air Force Medical University, Xi′an, China from January 2013 to March 2024 were collected. Their clinicopathological features and histological morphology were analyzed. The cases were further divided into 3 histologic subtypes. Follow-up information was collected to analyze the relationship between histological subtype and prognosis.Results:There were 5 males and 5 females in this cohort. The age of onset was 45-68 years, with a median age of 60.5 years. The polyp-involved sites included 2 cases in gastric fundus, 6 cases in gastric body, 1 case in gastric antrum, and 1 case in duodenum. Digestive endoscopy showed mucosal protrusion lesions in all cases, except 1 case (case 10) of shallow depression on the surface, with the maximum diameter ranging 0.5-2.5 cm. Endoscopic ultrasonography showed multilocular cystic low-density shadows, with septal enhancement (case 4). The preoperative clinical diagnosis was gastric polyp, ectopic pancreas or gastrointestinal stromal tumor. Two cases showed type 1 morphology (i.e., connected with the mucosa, with clear smooth muscle boundaries). One of them (case 10) had a clear opening to form a vase-like morphology, while the other (case 4) had no obvious opening with the surface mucosa. Three cases showed type 2 morphology (i.e., not connected with the mucosa, with clear smooth muscle boundaries). Five cases showed type 3 morphology (i.e., not connected with the mucosa, without clear smooth muscle boundaries or hyperplastic smooth muscle that separated hyperplastic glands showing lobular configuration). Among them, one case of duodenal lesions (case 9) showed gastric type gland hyperplasia and expansion, including gastric fossa, gastric fundic gland and pyloric gland, with various arrangement and combination, accompanied by smooth muscle hyperplasia. In case 10, there was leiomyomatous proliferation in the stroma. The cases 2 and 4 had atypical glandular structures and cell morphology, but immunohistochemistry showed wild-type expression pattern of p53 and a Ki-67 proliferation index of less than 1%, suggesting that it was reactive atypia secondary to inflammation. The results showed that 3 cases had different gene mutations, and no recurrent gene change was identified. All patients survived without disease during the follow-up period of 1-130 months.Conclusions:HIHP is a benign lesion and has no consistently detectable genetic alterations. The histological characteristics of gastrointestinal polyps are complex. Especially, the types 1 and 3 of HIHP have unique gross and microscopic features, which require combination of proper endoscopic sampling and histological examination to correctly classify them.

Objective:To investigate the clinicopathological features, diagnosis, genetic alterations, and biological behaviors of hamartomatous inverted hyperplastic polyp (HIHP) in the gastrointestinal tract.Methods:The clinical, sonographic, endoscopic and pathologic data of 10 HIHP cases diagnosed at the First Affiliated Hospital of Air Force Medical University, Xi′an, China from January 2013 to March 2024 were collected. Their clinicopathological features and histological morphology were analyzed. The cases were further divided into 3 histologic subtypes. Follow-up information was collected to analyze the relationship between histological subtype and prognosis.Results:There were 5 males and 5 females in this cohort. The age of onset was 45-68 years, with a median age of 60.5 years. The polyp-involved sites included 2 cases in gastric fundus, 6 cases in gastric body, 1 case in gastric antrum, and 1 case in duodenum. Digestive endoscopy showed mucosal protrusion lesions in all cases, except 1 case (case 10) of shallow depression on the surface, with the maximum diameter ranging 0.5-2.5 cm. Endoscopic ultrasonography showed multilocular cystic low-density shadows, with septal enhancement (case 4). The preoperative clinical diagnosis was gastric polyp, ectopic pancreas or gastrointestinal stromal tumor. Two cases showed type 1 morphology (i.e., connected with the mucosa, with clear smooth muscle boundaries). One of them (case 10) had a clear opening to form a vase-like morphology, while the other (case 4) had no obvious opening with the surface mucosa. Three cases showed type 2 morphology (i.e., not connected with the mucosa, with clear smooth muscle boundaries). Five cases showed type 3 morphology (i.e., not connected with the mucosa, without clear smooth muscle boundaries or hyperplastic smooth muscle that separated hyperplastic glands showing lobular configuration). Among them, one case of duodenal lesions (case 9) showed gastric type gland hyperplasia and expansion, including gastric fossa, gastric fundic gland and pyloric gland, with various arrangement and combination, accompanied by smooth muscle hyperplasia. In case 10, there was leiomyomatous proliferation in the stroma. The cases 2 and 4 had atypical glandular structures and cell morphology, but immunohistochemistry showed wild-type expression pattern of p53 and a Ki-67 proliferation index of less than 1%, suggesting that it was reactive atypia secondary to inflammation. The results showed that 3 cases had different gene mutations, and no recurrent gene change was identified. All patients survived without disease during the follow-up period of 1-130 months.Conclusions:HIHP is a benign lesion and has no consistently detectable genetic alterations. The histological characteristics of gastrointestinal polyps are complex. Especially, the types 1 and 3 of HIHP have unique gross and microscopic features, which require combination of proper endoscopic sampling and histological examination to correctly classify them.