Plexiform angiomyxoid tumor of the stomach. Am J Surg Pathol. 2008;32:1910-1912; author reply 1912. [PMID: 18824895 DOI: 10.1097/pas.0b013e3181838fd1]

Endoscopic submucosal excavation for gastric plexiform fibromyxoma: A case report and systematic review of literature

Plexiform fibromyxoma (PF) is a rare mesenchymal tumor of which the pathogenesis and molecular changes are still unclear. Histologically, it is characterized by a cluster of bland spindle or ovoid cells growing in the mucoid or fibromyxoid stroma rich in small blood vessels. At present, surgical resection is the primary treatment for PF.

Plexiform angiomyxoid myofibroblastic tumor treated by endoscopic submucosal dissection: A case report and review of the literature

BACKGROUND

Plexiform angiomyxoid myofibroblastic tumor (PAMT) is a rare mesenchymal tumor characterized by multiple nodular plexiform growth patterns and an immunophenotype with myofibroblasts. The pathological characteristics, immunohistochemistry, diagnostic criteria, differential diagnosis, and gene-level changes of PAMT have been reported in many studies. At present, the main treatment for PAMT in the reported cases is surgery; only eight cases were treated via endoscopy (excluding 1 thoracoscopic resection), and the lesions were all smaller than 5 cm. There are no reports on the prognosis and follow-up of young patients with lesion sizes reaching 5 cm who undergo endoscopic submucosal dissection (ESD). Herein, we present the first case of a young patient with a lesion size reaching 5 cm who was diagnosed with PAMT via endoscopic submucosal dissection.

CASE SUMMARY

A 15-year-old young man with upper abdominal pain for 2 years presented to the Gastroenterology Department of our hospital. Painless gastroscopy showed a semicircular bulge approximately 5 cm in size in the lesser curvature near the cardia of the fundus; the surface was eroded, and shallow ulcers had formed. The pathological manifestations of the biopsy were spindle cell proliferative lesions with interstitial mucinous changes, and the surface mucosa showed chronic inflammatory changes with active lesions; immunohistochemistry showed smooth muscle actin (SMA) (+), CD117 (-), CD34 (-), DOG-1 (-), S-100 (-), and Ki67 (LI: < 1%). We performed ESD on the patient. The lesion that we removed was 5 cm × 4 cm × 2 cm in size. Pathologically, the resected tissue displayed typical manifestations, such as fat spindle-shaped fibroblasts and myofibroblast-like cells showing irregular nodular hyperplasia. Immunohistochemistry staining of the tumor cells revealed the following: CD34 (partially +), SMA (weakly +), CD117 (-), DOG-1 (-), S-100 (-), SDHB (+), PCK (-), and Ki67 (labelling index: 2%). There was no recurrence or metastasis during the 3-mo follow-up after the operation, and the treatment effect was good. We also performed a review of the literature on the clinical manifestations, pathological features, immunohistochemistry, and differential diagnosis of PAMT.

CONCLUSION

At present, the diagnostic criteria for PAMT are relatively clear, but the pathogenesis and genetic changes require further study. PAMT is benign in nature, and these patients are less likely to experience local or metastatic recurrence. The main treatment is still surgery if the lesion is in the stomach. Partial gastrectomy and distal gastrectomy are the most frequently performed surgical treatments for PAMT, followed by local resection, subtotal gastrectomy, and wedge resection. But for comprehensive evaluation of the disease, ESD can be considered a suitable method to avoid excessive treatment.

Plexiform fibromyxoma: Review of rare mesenchymal gastric neoplasm and its differential diagnosis

Plexiform fibromyxoma (PF) is a very rare mesenchymal neoplasm of the stomach that was first described in 2007 and was officially recognized as a subtype of gastric mesenchymal neoplasm by World Health Organization (WHO) in 2010. Histologically, PF is characterized by a plexiform growth of bland spindle to ovoid cells embedded in a myxoid stroma that is rich in small vessels. The lesion is usually paucicellular. While mucosal and vascular invasion have been documented, no metastasis or malignant transformation has been reported. Its pathogenesis is largely unknown and defining molecular alterations are not currently available. There are other mesenchymal tumors arising in the gastrointestinal tract that need to be differentiated from PF given their differing biologic behaviors and malignant potential. Histologic mimics with spindle cells include gastrointestinal stromal tumor, smooth muscle tumor, and nerve sheath tumor. Histologic mimics with myxoid stroma include myxoma and aggressive angiomyxoma. Molecular alterations that have been described in a subset of PF may be seen in gastroblastoma and malignant epithelioid tumor with glioma-associated oncogene homologue 1 (GLI1) rearrangement. The recent increase in publications on PF reflects growing recognition of this entity with expansion of clinical and pathologic findings in these cases. Herein we provide a review of PF in comparison to other mesenchymal tumors with histologic and molecular resemblance to raise the awareness of this enigmatic neoplasm. Also, we highlight the challenges pathologists face when the sample is small, or such rare entity is encountered intraoperatively.

Recent developments in gastroesophageal mesenchymal tumours

The pathologist's approach to gastroesophageal mesenchymal tumours has changed dramatically during the last 25 years. In particular, gastrointestinal stromal tumour (GIST) has evolved from a wastebasket mesenchymal tumour category to a precisely defined entity with an increasingly detailed genetic subclassification. This subclassification has brought gastrointestinal mesenchymal neoplasia into the realm of precision medicine, with specific treatments optimised for particular genetic subtypes. Molecular genetic data have also greatly improved our understanding of oesophageal mesenchymal tumours, including the discovery that so-called 'giant fibrovascular polyps' in fact represent a clinically distinctive presentation of well-differentiated liposarcoma. Here, we will focus on gastroesophageal mesenchymal tumours for which there have been recent developments in classification, molecular genetics or tumour biology: granular cell tumour, 'giant fibrovascular polyp'/well-differentiated liposarcoma, plexiform fibromyxoma, gastroblastoma and, of course, GIST.

Gastric plexiform fibromyxoma: A case report

BACKGROUND

Plexiform fibromyxoma (PF) is a rare mesenchymal tumor of the stomach. The clinical features of PF frequently include upper abdominal pain, abdominal discomfort, hematemesis, melena, pyloric obstruction and an upper abdominal mass. We herein report a case of PF resected by laparoscopic radical distal gastrectomy plus Roux-en-Y gastrojejunostomy.

CASE SUMMARY

The patient was admitted to hospital, due to a 1-wk history of an abdominal space-occupying lesion identified during a health examination. He underwent complete resection by laparoscopic radical distal gastrectomy plus Roux-en-Y gastrojejunostomy. During the operation, the tumor was located in the anterior wall of the gastric antrum (approximately 7 cm × 6 cm × 5.5 cm) and did not show evidence of invasion of the serosa. Histology showed that the tumor cells were oval fibroblast-like and spindle-shaped cells, with numerous thin-walled blood vessels and abundant myxoid stroma. Cellular atypia and mitosis were both rare. Immunohistochemistry showed that the tumor cells were immunoreactive for smooth muscle actin, S-100 and CD-10, but were negative for CD-117, CD-34, DOG-1, and ALK. In this case, S-100 was positive and no significant disease was observed during the follow-up period.

CONCLUSION

The fact that PF is a rare tumor with only a few cases in this region can lead to misdiagnosis of this entity and pose a real diagnostic challenge for general surgeons and pathologists when encountering such patients and differentiating PF from other primary tumors of gastric mesenchymal origin. Our report may help increase awareness of this rare, but important new disease entity.

Frequency of Plexiform Fibromyxoma relative to gastrointestinal stromal tumor: A single center study

Plexiform Fibromyxoma (PF) is an exceedingly rare mesenchymal tumor of the gastric antrum that was first described in 2007. PF is a close mimic of gastrointestinal stromal tumor (GIST) clinically and histopathologically, but the frequency of PF relative to GIST is unknown. Moreover, although likely benign, long-term follow-up of PF is limited due to its recent description and rarity. PF has not been reported in distal jejunum. 118 primary GISTs that were surgically resected at our center (2000-2019) were retrieved. The patients' age, gender, clinical presentation, tumor location, size and number, and the presence or absence of metastasis, were documented. Risk of progressive disease was assessed according to the published GIST risk stratification model. Two unique cases of PF were compared. One gastric PF has been followed-up for 8 years, and the other occurred in the distal jejunum. In the latter, the PF diagnosis was rendered after the case was re-reviewed for the study. Clinical presentation resembled GIST in both PF cases. 14% of GISTs showed high risk features or were clinically malignant, whereas the PF patient with 8-year follow-up was free of disease. Based on this study, PF may be under-recognized, with 1 to 2% (1.7%) of GIST-like tumors possibly representing PF. PF may involve variable segments of intestine similar to GIST. Given the remarkable clinical and histopathologic overlap with GIST but differing outcomes, awareness and cognizance of this rare entity, plexiform fibromyxoma, is required for proper patient care.

A rare case of plexiform fibromyxoma in stomach: FNA diagnosis with histological correlation and differential diagnoses

Plexiform angiomyxoma (PF) is a rare benign mesenchymal neoplasm that arises in the antrum and pyloric region of the stomach. To the best of our knowledge, there are only two prior endoscopic ultrasound guided fine needle aspiration cytology examples have been reported. We report a case of PF which was diagnosed via EUS FNA and later confirmed on resection specimen. Differential diagnoses of this tumor are discussed. Although diagnosis of plexiform fibromyxoma on FNA specimen is difficult, a good FNA specimen with subsequent careful morphological evaluation and immunohistochemical staining work-up makes this task possible.

An Update on Clinicopathological and Molecular Features of Plexiform Fibromyxoma

Plexiform fibromyxoma is a rare and newly described gastric mesenchymal tumor with only 121 reported cases in the literature. Our understanding of plexiform fibromyxoma requires updating since the first case has been reported by Takahashi et al. 12 years ago. The present review summarized reported cases in the literature, and both clinical and pathological aspects of plexiform fibromyxoma were comprehensively discussed. Plexiform fibromyxoma usually causes nonspecific or bleeding signs or symptoms, and therefore clinical recognition of the disease is challenging. Plexiform fibromyxoma is of benign nature without any metastasis or recurrence reported, and more conservative surgical treatment should be considered.

Pediatric plexiform fibromyxoma: A PRISMA-compliant systematic literature review

BACKGROUND

Plexiform fibromyxoma (PF) is a rare gastric mesenchymal tumor, with approximately 80 cases reported to date. Gastrointestinal stromal tumor, the most common primary mesenchymal tumor of the stomach, shows different biological and clinical characteristics between adult and pediatric patients.

OBJECTIVES

This systematic literature review was conducted to elucidate the pathological and clinical features of pediatric PF compared to adult PF.

METHODS

MEDLINE (1948 to March 2018) and EMBASE (1947 to March 2018) were searched, and all English articles that reported clinical data on PF patients were identified. Two authors independently reviewed the articles and extracted data to assess immunohistochemistry, sex, chief complaint, tumor size, tumor-related mortality, and tumor recurrence and metastasis.

RESULTS

A total of 41 reports with 80 PF patients (of whom 70 were adult PF and 10 were pediatric PF patients) confirmed by histological and immunohistochemical findings were included. Of a total of 80 tumors, 62 (78%) were located in the gastric antrum, 42 (65%) presented with ulceration, and 48 (74%) were resected by partial gastrectomy. Median tumor size of the resected specimen was larger in pediatric PF than in adult PF cases (5.3 cm vs 4.0 cm, P = .036). However, there was no difference between pediatric and adult PFs in immunohistochemical expression, sex predominance, chief complaint, tumor-related mortality, and tumor recurrence and metastasis during the follow-up periods.

CONCLUSION

Other than increased tumor growth in pediatric PFs, PF is a single disease entity with similar pathological features and benign clinical behavior regardless of onset age.

Plexiform fibromyxoma of the small bowel: A case report

BACKGROUND

Plexiform fibromyxoma is a rare, special type of mesenchymal tumor. The most common presenting symptoms are anemia, hematemesis, and hematochezia, without sex or age predilection. The reported cases have mainly occurred in the gastric antrum and pylorus region, with some cases in the duodenum.

CASE SUMMARY

We report here a case of plexiform fibromyxoma in the upper segment of the jejunum, which was continuously followed up for 3 years after surgical removal. Plexiform fibromyxoma showed multinodular or plexiform growth. The cells in the tumor node were spindle-shaped but few in number and mitotic figures. Small blood vessels and mucous matrix were found among the tumor cells. Immunohistochemistry revealed that the plexiform fibromyxoma cells were positive for smooth muscle actin, focally positive for CD10, and negative for cytokeratin, CD117, DOG-1 (discovered on GIST-1) desmin, S-100, epithelial membrane antigen, and CD34. Ki-67 labeling index was < 5%. Plexiform fibromyxoma showed benign biological behavior. After 3 years of consecutive postoperative follow-up, no obvious signs of metastasis or recurrence were found by imaging examination.

CONCLUSION

Plexiform fibromyxoma is a rare type of mesenchymal tumor. The diagnosis mainly depends on pathological examination, and it should be distinguished from other gastrointestinal mesenchymal tumors.

Plexiform Angiomyxoid Myofibroblastic Tumor of the Stomach: a Rare Case

Plexiform angiomyxoid myofibroblastic tumor (PAMT) of the stomach is a very rare mesenchymal tumor of the gastrointestinal tract. We report a case of asymptomatic gastric PAMT that was pathologically confirmed after surgical resection. The tumor had a multinodular plexiform growth pattern, bland-looking spindle cells, and an Alcian blue-positive myxoid stromal matrix rich in small blood vessels. Immunohistochemistry analysis revealed that the tumor cells of the PAMT were positive for smooth muscle actin (SMA) and negative for c-kit, CD34, S-100 protein, epithelial membrane antigen (EMA), and desmin. PAMT should be differentiated from other submucosal tumors of the stomach by immunohistochemical findings. Considering the benign features of this tumor, observation without resection may be an option for the treatment of PAMT if the tumor is asymptomatic.

Computed tomography and magnetic resonance imaging of a plexiform angiomyxoid myofibroblastic tumor: a case report

Background

Plexiform angiomyxoid myofibroblastic tumor (PAMT) is a very rare mesenchymal tumor of the stomach. Here we report a case of pathologically confirmed PAMT with an unique cyst formation.

Case presentation

A 55-year-old male with a 10-year history of a gastric subepithelial tumor underwent computed tomography (CT) and magnetic resonance imaging (MRI). Two cysts were observed in the tumor, and the cyst wall showed moderately high intensity on T2-weighted images compared with the gastric wall. On dynamic study, the cyst wall showed a gradual enhancement pattern, and prominent enhancement was observed in the delayed phase. Laparoscopic partial gastric resection was performed, and a pathological diagnosis of PAMT was rendered.

Conclusion

We present a rare case of gastric PAMT, which was uniquely presented as cysts. One of the cysts in the tumor had an epithelial wall lining, which had never been reported before in gastric mesenchymal tumor, in addition to partial glandular structure. We reviewed our case, focusing on radiologic-pathologic correlation, and suggested hypothesis of cyst formation. According to our findings, PAMT with cyst formation would be included of differential diagnosis of gastric subepithelial tumors.

A rare case of plexiform angiomyxoid myofibroblastic tumor in the stomach which was diagnosed at the earliest stage in the literature

Plexiform angiomyxoid myofibroblastic tumor (PAMT) is a rare gastric mesenchymal entity with a peculiar plexiform pattern, bland spindle cells and myxoid stroma rich in arborizing blood vessels. Here we report a 44-year-old Chinese woman with PAMT. Initially she was admitted for removal of a gastric antral‘polyp’ found on a routine examination 5 months previously. Our gastroscopy showed a 0.8 × 0.8 cm polyp-like mass in the antrum which protruded into the lumen. Endoscopic submucosal dissection (ESD) was performed to remove this mass en bloc. The specimen was carefully examined by pathologists, and the correct diagnosis of PAMT was finally made. The tumor in this case depicted typical histopathological and immunohistochemical features of gastric PAMT. This PAMT was not only the smallest on endoscopic examination in the literature but also—unlike the already reported PAMTs—exhibited a focal hyperechogenic lesion on endoscopic ultrasonography (EUS). This information highlights its value on how to identify a PAMT at its early stage.

Unusual focal keratin expression in plexiform angiomyxoid myofibroblastic tumor: A case report and review of the literature

BACKGROUND

Plexiform angiomyxoid myofibroblastic tumor (PAMT), also known as plexiform fibromyxoma, is a rare distinctive benign intramural tumor, typical of gastric antrum, commonly causing mucosal ulceration with upper gastrointestinal bleeding and anemia, effectively treated by complete surgical resection usually accomplished by distal gastrectomy.

METHODS AND RESULTS

We herein report a 47-year-old man presenting with a syncopal episode, regurgitation and epigastric discomfort, bearing a gastric antral myxoid plexiform tumor positive for α-smooth muscle actin, vimentin and, partially, for caldesmon, desmin, and CD10; CD117, DOG1, CD34, S100, CAM5.2, CK20, CK7, EMA, p53, CDX2, chromogranin A, synaptophysin, anaplastic lymphoma kinase, Melan-A, and HMB-45 were all negative. All these features are typical of PAMT. Of note, focal positivity for AE1/AE3 and pan-CK KL1 was also present.

CONCLUSIONS

The finding of a focal keratin expression in PAMT contributes to enlarge the immunophenotypic spectrum of this tumor type and is relevant for avoiding presurgical misdiagnoses which could ultimately lead to inappropriate overtreatment of patients with PAMT.

Recurrent MALAT1-GLI1 oncogenic fusion and GLI1 up-regulation define a subset of plexiform fibromyxoma

Plexiform fibromyxomas are rare neoplasms, being officially recognized as a distinct entity among benign mesenchymal gastric tumours in the 2010 WHO Classification of Tumours of the Digestive System. Characteristically, these tumours have a multinodular/plexiform growth pattern, and histologically contain variably cellular areas of bland myofibroblastic-type spindle cells embedded in an abundant myxoid matrix, rich in capillary-type vessels. As yet, the molecular and/or genetic features of these tumours are unknown. Here we describe a recurrent translocation, t(11;12)(q11;q13), involving the long non-coding gene metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and the gene glioma-associated oncogene homologue 1 (GLI1) in a subgroup of these tumours. The presence of the fusion transcript in our index case was confirmed using polymerase chain reaction (PCR) on genomic DNA, followed by Sanger sequencing. We showed that the truncated GLI1 protein is overexpressed and retains its capacity to transcriptionally activate its target genes. A specific FISH assay was developed to detect the novel MALAT1-GLI1 translocation in formalin-fixed, paraffin-embedded (FFPE) material. This resulted in the identification of two additional cases with this fusion and two cases with polysomy of the GLI1 gene. Finally, immunohistochemistry revealed that the GLI1 protein is exclusively overexpressed in those cases that harbour GLI1/12q13 genomic alterations. In conclusion, overexpression of GLI1 through a recurrent MALAT1-GLI1 translocation or GLI1 up-regulation delineates a pathogenically distinct subgroup of plexiform fibromyxomas with activation of the Sonic Hedgehog signalling pathway. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Plexiform fibromyxoma with cotyledon-like serosal growth: A case report of a rare gastric tumor and review of the literature

Plexiform fibromyxoma is a rare, benign mesenchymal neoplasm that predilects the gastric antrum and has potential for misdiagnosis as a gastrointestinal stromal tumor (GIST). The histology of the tumor is characterized by interwoven fascicular growth of cytologically bland spindled cells within a variably myxoid stroma. The current study reports the clinicopathological and immunohistochemical findings of a plexiform fibromyxoma resected from a 28-year-old Vietnamese female. The patient presented with acute, severe abdominal pain and worsening anemia. The initial fine-needle aspiration and needle core biopsy of the gastric antral mass led to an initial diagnosis of GIST. The subsequent distal partial gastrectomy revealed a 5.5-cm transmural antral mass that ulcerated the overlying mucosa and grew as variably elongated, myxoedematous, polypoid (cotyledon-like) excrescences from the serosal surface. Microscopically, the tumor demonstrated plexiform and multinodular growth of cytologically bland spindled cells proliferating in an abundant myxocollagenous stroma with a prominent capillary network. Tumor cells immunohistochemically expressed smooth muscle actin and CD10, but did not express CD117, Discovered on GIST-1 or nuclear β-catenin. Follow-up evaluation 23 months post surgery revealed no evidence of residual tumor. A review the cases of this rare entity reported in the English language literature is also provided.

Plexiform angiomyxoid myofibroblastic tumour of the duodenum: a rare entity

Plexiform angiomyxoid myofibroblastic tumour (PAMT) has recently emerged as a new entity among gastrointestinal mesenchymal tumours. All of the 27 cases reported until now originated from the stomach. We report the first case of a duodenal PAMT arising from the first part of the duodenum in a 19-year-old woman presenting with upper abdominal pain and an abdominal lump.

Plexiform fibromyxoma: report of two pediatric cases and review of the literature

Plexiform fibromyxoma is a distinctive mesenchymal neoplasm usually arising in the gastric antrum. We report 2 cases of this entity in pediatric patients, including the first case arising in the esophagus. The patients were a 16-year-old female who presented with chest pain and was found on computed tomographic scan to have a midesophageal mass at the level of the carina, and an 11-year-old female with a gastric mass. Both patients underwent surgical resection of their tumors, which histologically exhibited a plexiform growth pattern with multiple nodules in the muscularis propria and infiltrative borders. The nodules were composed of a rich myxoid stroma with bland uniform spindle cells, no mitoses or necrosis, and delicate blood vessels in the background. Immunohistochemical studies demonstrated that the tumor cells were immunoreactive with smooth muscle actin and not reactive with S-100, CD34, desmin, and c-kit (CD117). We report the first case of plexiform fibromyxoma originating in the esophagus, emphasize its occurrence in pediatric patients, and review the related literature.

Mesenchymal Tumors of the Gastrointestinal Tract Other than GIST

Mesenchymal tumors involve the gastrointestinal (GI) tract more frequently than other visceral organs. Many such tumors are small, and are benign and increasingly being detected incidentally during colonoscopic screening. Some tumors show distinctive features at this site, such as schwannoma and clear cell sarcoma-like tumor of the GI tract. Without knowledge of these features, recognition of these tumor types can be difficult. This reviews addresses recent developments and diagnostic features of mesenchymal tumors of the GI tract other than gastrointestinal stromal tumor (GIST).

Plexiform angiomyxoid myofibroblastic tumor of the stomach: report of two cases and review of the literature

Plexiform angiomyxoid myofibroblastic tumor (PAMT) of the stomach is a recently recognized entity. Because of its rarity, only 22 cases have been reported in the English-language literature and most of these are single case reports. We report two cases of gastric PAMT. The tumor cells were bland and plexiform arranged in a myxoid stroma, which was positive for alcian blue. Immunohistochemically, the tumor cells were positive for smooth muscle actin, but negative for c-kit, CD34, desmin, S-100 protein, epithelial membrane antigen, neurofilament, and protein kinase C-theta. Mutation analyses for exon 9, 11, 13, and 17 of KIT genes and 12, 14, and 18 of the platelet-derived growth factor receptor alpha (PDGFRA) genes were performed and the tumors were wild-type for mutation.

Selected unusual tumors of the stomach: a review

Several unusual stomach tumors have been recently described. In addition, some tumors that are often encountered in other sites may rarely occur as primary gastric tumors. The diagnostic surgical pathologist needs to be aware of some of these lesions to prevent misdiagnosis. This overview discusses the key clinical features, pathology, immunohistochemistry, and relevant molecular findings of multiple minute gastrointestinal stromal tumors and interstitial cell of Cajal hyperplasia, nerve sheath tumors (schwannoma and perineurioma), gastroblastoma, granular cell tumor, glomus tumor, plexiform angiomyxoid myofibroblastic tumor, and primary clear cell sarcoma of the gastrointestinal tract that occur as primary gastric neoplasms.

Plexiform angiomyxoid myofibroblastic tumor of the stomach: a case report

Plexiform angiomyxoid myofibroblastic tumor (PAMT) is a recently described mesenchymal tumor of the stomach. We report the first case of PAMT in Korea. A 52-yr-old man underwent esophagogastroduodenoscopy due to dyspepsia for 2 yr. There was a submucosal mass with small mucosal ulceration in the gastric antrum. The tumor measured 3.5 × 2.3 cm in size and showed multinodular plexiform growth pattern of bland-looking spindle cells separated by an abundant myxoid or fibromyxoid matrix rich in small thin-walled blood vessels. The tumor cells were negative for CD117 (c-KIT), CD34 and S-100 protein, but diffusely positive for smooth muscle actin consistent with predominant myofibroblastic differentiation. The patient is doing well without recurrence or metastasis for 5 months after surgery. Although there have been limited follow-up data, PAMT is regarded as a benign gastric neoplasm with histological and immunohistochemical characteristics distinguished from gastrointestinal stromal tumor and other mesenchymal tumors of the stomach.

Gastric plexiform angiomyxoid myofibroblastic tumor

Plexiform angiomyxoid myofibroblastic tumor (PAMT) is a relatively recently described gastric tumor with a peculiar plexiform growth pattern. PAMT is typified by a myofibroblastic immunophenotype that distinguishes it from the more common gastrointestinal stromal tumors and the rarely documented fibromyxomas. We report an additional PAMT, the seventh tumor with this label, which was an incidental finding on abdominal computed tomography scan of a 35-year-old Indian female. The tumor measured 4 x 3 x 2 cm and demonstrated plexiform architecture, myxoid stroma, prominent vasculature and spindled cells with myofibroblastic differentiation. The clinicopathological features, progesterone immunopositivity, hitherto undocumented, and mimicry of other primary and secondary gastric mesenchymal tumors, including endometrial stromal sarcoma, are discussed.

Plexiform angiomyxoid myofibroblastic tumor of the stomach

Plexiform angiomyxoid myofibroblastic tumor of the stomach is a unique mesenchymal tumor that we first described in 2007. The tumor is very rare, and to date, only 18 cases confirmed by immunohistochemistry have been reported in the literature. The patients’ ages ranged from 7 to 75 years (mean, 43 years), and the male-to-female ratio was approximately 1:1. Representative clinical symptoms are ulceration, associated upper gastrointestinal bleeding (hematemesis), and anemia. The tumors are located at the antrum in all cases, and grossly, the tumor is whitish to brownish or reddish, and forms a lobulated submucosal or transmural mass. Microscopically, the tumor is characterized by a plexiform growth pattern, the proliferation of cytologically bland spindle cells, and a myxoid stroma that is rich in small vessels and positive for Alcian blue stain. Immunohistochemically, the tumor cells are positive for α-smooth muscle actin and negative for KIT and CD34. Differential diagnoses include gastrointestinal stromal tumor and other mesenchymal tumors of the gastrointestinal tract. Some authors proposed that this tumor should be designated as “plexiform fibromyxoma”, but this designation might cause confusion. The tumor is probably benign and thus far, neither recurrence nor metastasis has been reported.

Plexiform fibromyxoma: a distinctive benign gastric antral neoplasm not to be confused with a myxoid GIST

A great majority of gastric mesenchymal tumors are gastrointestinal stromal tumor (GIST). A rare group of non-GISTs include myxoid mesenchymal neoplasms. In this report, we describe 12 cases of a distinctive gastric tumor, named here as plexiform fibromyxoma. These tumors occurred in 5 men and 7 women of ages 7 to 75 years (median, 41 y). All tumors were located in the gastric antrum and 6 of them also extended into extragastric soft tissues or into the duodenal bulb. The tumors measured from 3 to 15 cm (median, 5.5 cm). Histologically typical was a plexiform intramural growth with multiple micronodules containing paucicellular to moderately cellular myxoid to collagenous and fibromyxoid neoplastic elements. A prominent, sometimes plexiform capillary pattern was typically present. Extramural components included subserosal nodules, and sometimes more cellular, solid nonplexiform spindle cell proliferation. The tumor cells varied from oval to spindled and had limited atypia and mitotic activity < 5/50 high-power fields. Frequent ulceration, mucosal invasion, and vascular invasion (4 cases) had no adverse significance in these tumors. Immunohistochemically, the tumor cells were positive for alpha smooth muscle actin, and variably for CD10, and were consistently negative for KIT, DOG1, CD34, desmin, and S100 protein. No KIT or platelet-derived growth factor receptor alpha mutations were present in the 3 examined cases. None of the 4 patients who were followed from 9 to 20 years (median, 19 y) developed recurrences or metastases. Additional 3 patients survived 14 to 25 years with unknown tumor status. Review of large numbers of mesenchymal tumors in the esophagus and intestines did not reveal similar tumors. Plexiform fibromyxoma is a distinctive benign gastric antral neoplasm that should be separated from GIST, nerve sheath tumors, and other fibromyxoid neoplasms.