An LHPC, which was first formally described as a new entity in the 2002 edition of the WHO classification of soft-tissue tumors, is a rare hemangiopericytoma variant composed of mature adipocytes and hemangiopericytoma-like areas[20
]. LHPC was first described as a unique hemangiopericytoma variant by Nielsen et al[1
] and was named “LHPC” in the English language literature in 1995. In 2000, Guillou et al[4
] noted that LHPCs and solitary fibrous tumors (SFTs) share similar clinical, pathological, immunohistochemical, and ultrastructural features, except for the presence of mature adipocytes in LHPC, and suggested that LHPC does not correspond to a well-defined entity but, rather, represents a fat-containing variant of SFT.
To date, a total of 50 pathologically confirmed cases of LHPC have been reported, including our patient[1-19
]. Most lesions presented clinically as long-standing, deep-seated, indolent tumors, discovered fortuitously in some patients, whereas others had symptoms of compression related to tumor enlargement[4
]. As documented in Table , LHPC seems to occur in middle-aged adult patients (range, 21-79 years; mean, 51.7 years), similar to the mean age of 55 years reported by Folpe et al[3
]. The sex distribution for the LHPC cases for which this information is known is 20 females and 29 males, demonstrating a slight male predilection of LHPC. The size of the lesions ranged from 0.8 cm to 21 cm (mean, 7.9 cm). LHPCs have a wide anatomical distribution, but the most commonly affected sites are the lower extremities (14/50), including the thigh, hip, calf, popliteal fossa, and inguina. Other sites (72%) included the retroperitoneum, orbit, mediastinum, and pelvic cavity. The thigh, retroperitoneum and the orbit were the most commonly affected sites. Most of the tumors were located in the deep soft tissue[4
Given that no LHPC patients developed recurrence during the follow-up interval and that all were without disease, some authors have concluded that LHPCs are likely to be benign tumors[3,4
]. However, in our opinion, their biological behavior has yet to be determined because only 30 cases have been followed up in the English language literature to date, and the mean follow-up length was only 30.5 mo, not long enough to draw definitive conclusions about the prognosis of LHPCs. Davies et al[5
] suggested that patients with LHPC should be followed up for more than 10 years.
Grossly, LHPC generally presents as a well-demarcated, variably encapsulated, medium-sized mesenchymal tumor. Cut sections show alternating areas of whitish and yellowish tumor tissue, in most cases with a lobular or fascicular appearance. Microscopically, the tissue characteristically shows a varying combination of cellular areas composed of round to spindle cells, collagenous or myxoid stroma with focal sclerotic areas, hemangiopericytoma-like vasculature made of small- to medium-sized thick-walled branched vessels, and lipomatous areas made up of mature adipocytes[4
]. LHPCs may become large and occasionally show nuclear atypia within sclerotic zones, a phenomenon probably akin to that seen in degenerated schwannomas. LHPCs may also rarely show foci of high cellularity but do not approach the level seen in malignant LHPCs or in other malignancies that commonly show a hemangiopericytomatous pattern, such as synovial sarcoma or mesenchymal chondrosarcoma[3
]. Immunohistochemistry showed that the nonadipocytic tumor cells are strongly and diffusely positive for vimentin and CD34, and they can also be positive for CD99 and bcl-2[21
]. Ultrastructurally, the nonadipocytic tumor cells show features consistent with fibroblastic, myofibroblastic or pericytic differentiation[21
Considering the location and histological appearance of this type of tumor, the main differential diagnoses considered should include GIST, angiomyolipoma, liposarcoma, and spindle cell lipoma (SCL). The stomach is the most common location for GIST, with 60%-70% of tumors occurring in this location[22
]. In fact, in our study, the initial clinical diagnosis was GIST. Briefly, GISTs contain bundles of spindle cells and do not contain the mature adipocytes characteristic of LHPC. LHPCs are positive for CD34 but are negative for CD117. In contrast, GISTs are positive for CD117, CD34, and PDGFRA[23
]. There was consistent negative staining for CD117 and PDGFRA. Hence, the tumor was not a GIST but, judging by its histological and immunohistochemical features, an LHPC. Differentiating an angiomyolipoma, especially one with a prominent smooth muscle component, from an LHPC is based on the former’s distinctive arrangement of the spindle cells around thick-walled vessels and their immunoreactivity for SMA and melanocytic markers (HMB45 and melan-A)[4,9
]. Liposarcoma, especially the myxoid variant, can have a prominent vasculature. The vascular configuration should serve as a useful clue in distinguishing between liposarcoma and LHPC. The vessels in myxoid liposarcoma form a delicate plexiform capillary vascular network, unlike the staghorn pattern of LHPC. Furthermore, LHPCs are devoid of lipoblasts[1
]. SCL usually develops in the subcutaneous tissue of the neck and upper back of male patients and contains short bundles of wiry collagen admixed with the spindle cells. SCLs do not contain the hemangiopericytoma-like vasculature of LHPCs[21
In conclusion, the clinicopathological features of our case were entirely compatible with those of LHPC, and to our knowledge, this is the first reported case affecting the stomach. More cases of LHPC of the stomach must be studied to draw definitive conclusions about its distinct behavior and management.