Unusual focal keratin expression in plexiform angiomyxoid myofibroblastic tumor

Abstract

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.

Gastroblastoma harbors a recurrent somatic MALAT1–GLI1 fusion gene

“…However, plexiform fibromyxoma is clinically benign and lacks biphasic morphology, quite different from gastroblastoma. 7,[28][29][30][31][32][33][34][35][36] We strongly suspect that the presence of MALAT1-GLI1 fusions in both of these tumors represents simply another example of identical genetic events in unrelated neoplasms, akin to the PAX3-FOXO1 or PAX3-NCOA1 fusions that may be seen in biphenotypic sinonasal sarcomas and alveolar rhabdomyosarcomas, 37,38 or the EWSR1-ATF1 fusions seen in clear cell sarcoma and angiomatoid fibrous histiocytoma (among others). [39][40][41] In conclusion, we have identified a recurrent oncogenic fusion gene in gastroblastoma, MALAT1-GLI1.…”

Rarity among benign gastric tumors: Plexiform fibromyxoma - Report of two cases

“…PFMs are very rare gastric mesenchymal tumors. To date, various names have been proposed to describe this benign spindle cell tumor, including fibromyxoma, plexiform angiomyxoid tumor, and PAMT[ 2 , 6 ]. In 2009, Miettinen et al[ 4 ] described 12 cases of benign gastric antral fibromyxoid tumors, designating them as PFM.…”

“…Immunohistochemically, tumor cells usually show focal to diffuse positive reaction with vimentin, α-SMA and CD10, and sometimes with desmin and/or h-caldesmon or calponin[ 2 , 4 - 6 , 9 , 10 ]. This immunoprofile indicates that these tumors contain cells with myofibroblastic and fibroblastic and/or smooth muscle cell characteristics, all of which were observed as present in one of our cases.…”

“…However, the predominant cell type is myofibroblastic in the majority of the reported cases. Quero et al[ 6 ] compiled the clinicopathologic characteristics of all cases published up to March 2016. We present in Table 1 the collective immunohistochemical findings for desmin and h-caldesmon/calponin, as well as the findings for the two newest cases presented herein.…”

“…In all of these tumor types, negativity for immunohistochemical staining with KIT, DOG1, CD34, epithelial membrane antigen, beta-catenin and S100 has been reported[ 2 , 4 - 6 , 9 , 10 ]. A negative finding for KIT and DOG1 excludes GIST, especially for the plexiform myxoid type, while a negative finding for S100 excludes neuronal tumors ( i.e ., schwannoma and neurofibroma).…”