Pathological evaluation of percutaneous tumor biopsy tissue (Fig. 3a–g) suggested a diagnosis of HEHE, with proliferation of acidophilic tumor cells surrounded by a fibromyxoid stroma (Fig. 3a); strong immunohistochemical staining for CD31 (Fig. 3b), CD34 (Fig. 3c), AE1/3 (Fig. 3d), and CAMTA1 (Fig. 3e); and weak staining for D2-40 (Fig. 3f) with a Ki-67 labeling index < 10% (Fig. 3g). The gene discussed is PECAM1; the disease is neoplasm.