Plexiform Angiomyxoid Tumor of the Stomach


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To the Editor:We read with great interest the recent article by Takahashi et al4 regarding an unusual mesenchymal neoplasm of the stomach. The authors described 2 examples of a gastric tumor they termed “plexiform angiomyxoid myofibroblastic tumor” that occurred in 2 men. The tumors showed a peculiar plexiform growth pattern and were composed of uniform, bland spindle cells. The tumoral stroma contained abundant myxoid matrix and conspicuous small vessels. The tumors were immunohistochemically negative for c-kit, CD34, and S-100, while they labeled for α-smooth muscle actin (SMA) and muscle actin. We recently encountered 2 similar cases in our consultation practice and wish to communicate these additional examples.REPORT OF CASESCase 1 was a 19-year-old woman presenting with a mass in the stomach. Distal gastrectomy was performed and showed a 4.5×3.5×3 cm lobulated tan-white mass with a glistening cut surface in the antrum. The tumor involved submucosa, muscularis propria, and subserosa, and the serosal surface was studded with multiple polypoid projections of the tumor.Case 2 was a 46-year-old man who presented with upper gastrointestinal bleeding. Endoscopy revealed an ulcer in the gastric antrum with a deeply infiltrating mass detected by ultrasound. The patient underwent distal gastrectomy. The specimen showed a 3.5 cm finely lobulated tan-white mass transmurally involving the gastric wall and associated with an overlying 1 cm ulcer.Microscopic examination of the both lesions demonstrated virtually identical findings. The tumors grew in an irregular multinodular plexiform fashion, widely dissecting the entire thickness of the stomach wall (Fig. 1A). They consisted of a relatively hypocellular spindle cell proliferation. The tumor cells were disposed randomly or in a vaguely fascicular fashion, separated by an abundant myxoid stroma rich in capillary-sized vessels (Fig. 1B). Areas of delicate collagenization were noted, particularly in the center of the tumor nodules (Fig. 1C). No necrosis or vascular invasion was seen. The constituent cells showed oval dark nuclei with smooth contours and had indistinct cytoplasmic borders. Rarely, cells with blunted nuclear ends and thin long eosinophilic cytoplasmic extensions were seen, reminiscent of smooth muscle cells. Mitotic figures were not appreciated in case 1, and rarely noted (<1/50 high-power field) in case 2. Immunohistochemically, the tumor cells were negative for CD117, platelet-derived growth factor receptor α (PDGFRA), CD 34, and S-100 protein. Case 1 was also negative for epithelial membrane antigen, collagen type IV, laminin, estrogen receptor, progesterone receptor, and CD10. Case 2 was negative for AE1:AE3 and bcl-2. The majority of the tumor cells in both cases labeled for HHF-35 and SMA in dense cytoplasmic pattern, whereas focal staining for desmin was noted. In case 2, a subset of tumor cells was also immunopositive for caldesmon and calponin. The Ki-67 labeling index in case 2 was less than 1%. No mutation was identified in either case in KIT (exons 9, 11, 13, and 17) or PDGFRA (exons 12 and 18) by direct sequencing using paraffin-embedded tissue. There is no recurrence or metastasis in the short-term follow-up in each case, at 9 months (case 1) and 4 months (case 2) after the procedure.DISCUSSIONThe tumors we describe here closely resemble the reported cases with regard to location, growth pattern, cellular architecture, cytologic features, and immunoprofile,4 and we believe they all represent the same entity. As was discussed in the previous report, the main differential diagnostic consideration included gastrointestinal stromal tumor (GIST), peripheral nerve sheath tumor, and leiomyoma.

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