Giant cell angioblastoma (GCAB) is an extremely rare soft tissue tumor of children. Diagnosis can be made according to the unique morphological characteristics, which include nodular, linear, and plexiform aggregates of oval- to spindle-shaped tumor cells interspersed with large mononuclear cells and multinucleate giant cells [1]. Since the first case of GCAB reported in 1991 [1], only one report described the other three cases of GCAB in infants occurring in the central palate, hypothenar portion of the right hand, and on the scalp, respectively [2]. We had reported the fifth case in the world of GCAB [3]. The involved tissues of GCAB in human pediatric patients have been reported as skin and soft tissue, including a substantial portion of an upper extremity [1], mucous membranes of the central palate, skin of the scalp, subcutaneous soft tissue of the right hypothenar eminence extending along the metacarpals [2], and leg bone [3]. Considering the extremely few case reports of GCAB worldwide, it is critical to include more case reports in the literature to increase our understanding of the clinicopathological features of GCAB. Here, we present the sixth GCAB case, which is quite different from the other five cases and occurred in the bone at the early childhood.

Iinterferon-alpha (IFN-α) has been successfully used as an antitumor therapeutic agent [4] and has shown robust antiangiogenic properties [5]. IFN-α has been used to treat two GCAB patients and showed remarkable wound healing properties after operative therapy, even promoting regeneration of bone [6].

Histological differential diagnosis mainly involves other vascular neoplasms accompanying giant cell proliferation, such as giant cell fibroblastoma [7], angiomatoid fibrous histiocytoma [8], plexiform fibrohistiocytic tumor [7, 9]. The giant cells in Giant cell fibroblastoma are characteristically located in the inner-side of the cranny-like vasculature and CD34-positive, which is different from GCAB. Angiomatoid fibrous histiocytoma exhibits stretched tumor cells that are compartmentalized by cystic dilated vessel-like lumen, and have a compact envelope surrounded by abundant lymphocytes. Plexiform fibrohistiocytic tumors also form multiple nodulars, but lack vasculature and do not conform to hemangioma structures. The proliferated cells in plexiform fibrohistiocytic tumors are mononuclear histiocytes and fibroblasts. The osteoclast-like giant cells that sparked in the tumor lack clear, large nucleoli.

Intravascular lesions, such as reactive neoplastic lesions, with organized thrombus accompanied by central foreign material and an associated foreign body giant cell reaction should be carefully considered during diagnosis, and patient age and case history may help to distinguish the underlying disease [10]. In addition, as our case was derived from the tibia, it was important to rule out adamantinoma. Adamantinoma is characterized by biphasic epithelial and osteofibrous components and rarely occurs in children (median age at diagnosis: 25 to 35). Both of these features may be used to differentiate adamantinoma from GCAB [11]. Some of the malignant mesenchymomas, including leiomyosarcoma, rhabdomyosarcoma, chondrosarcoma, osteosarcoma and myxomatous components, should also be considered as differential diagnoses [12], and are distinguishable from GCAB by its lack of malignancy.

The prognosis of GCAB is not yet defined. Our follow-up to date has suggested that the prognosis of GCAB was relatively good but varied with site, patient age and the adjacent tissue infiltration. Tumor penetration of bone and infiltration of soft tissues might indicate early recurrence. And adjacent tissue infiltration would likely be the most significant marker for poor prognosis. Interferon-α therapy has been suggested as a preventative therapy against GCAB recurrence [2, 6]. Neither of our two cases received IFN-α therapy, and the first case has shown no signs of recurrence within the three years of follow-up [3]. But this case recurred seventeen months after en bloc resection. Comparing the infiltrate condition of our two cases with all the other four reported cases led us to conclude that GCAB could be divided into two subtypes. Type I, as exemplified by our first case, occurs earlier, does not infiltrate surrounding tissues, and has good prognosis. Type II, as exemplified by the current case, occurs later and infiltrates the surrounding tissues, and is expected to relapse earlier and have worse prognosis. Type I could transform into Type II over long-term development. And IFN-α therapy may benefit for type II of GCAB.

Our newly identified case of GCAB supports that GCAB as a distinct and rare angiogenic tumor in infants with local infiltration potential. We summarized the six collective GCAB cases reported to date and distinguished them into two subtypes. Diagnosing and distinguishing the subtypes of GCAB is meaningful for estimating prognosis and guiding therapy. Infiltration status is likely a key prognostic indicator of GCAB. A definite diagnosis followed by complete excision might facilitate better prognosis of GCAB. Interferon-α therapy benefits type II GCAB patients.

Written informed consent was obtained from the patient for publication of this Case Report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.