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

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.

Figure 1

Pathological findings of the resected mass. (A) The resected specimen revealed a 60 mm lobulated intramural antral mass with a reddish gelatinous cut surface. (B, C) Histology of the tumor showed a plexiform intramural neoplasm displaying an alcian-positive myxoid matrix, with an arborizing capillary network (B, hematoxylin and eosin; C, alcian blue). (D–F) Immunohistochemistry of the tumor showed expression of α-smooth muscle actin (D) and partial positivity for caldesmon (E) (note the positive control of the intensely stained muscularis propria—bottom in D, bottom right in E), and focal positivity for cytokeratins AE1/AE3, sometimes with a perinuclear or a dot-like pattern (F).