Using Denosumab as a Nonsurgical Management of Aneurysmal Bone Cysts in the Pelvis.

Background: Aneurysmal bone cysts (ABCs) are infrequent, benign, and locally destructive lesions that most commonly occur during the first two decades of life. They usually affect the metaphysis of the long bones, but the pelvis is involved in 8%-12% of the cases. The management of pelvic ABCs is a challenging issue due to difficulties in choosing the appropriate approach, adjacent neurovascular bundles, the risk of intraoperative bleeding with difficulty achieving good hemostasis, and the risk of injury to the hip or sacroiliac joints. Limited data exist concerning the use of denosumab as a non-surgical treatment for pelvic ABCs. Our hypothesis was that denosumab might be an effective and safe solo treatment of cases with ABCs in the pelvis. Methods: We retrospectively assessed 20 patients with ABCs in the pelvis, who were treated by denosumab as a solo agent without surgery. Patients were assessed regarding disease control, the incidence of recurrence and non-oncological complications, and functional outcome. Results: The mean follow-up period was 38.5 months. Disease control was achieved in 16 patients (80%), with no local recurrence. Tolerable drug-related complications occurred in 15% of cases. The mean Musculoskeletal Tumor Society score was 92.3%. Conclusions: Denosumab may provide a reliable option in the nonsurgical treatment of ABCs of pelvic origin with expected lower morbidity than the surgical solution and tolerable complications. Further studies on the safety profile and long-term effects of denosumab especially in skeletally immature patients are required.

Surgical Management and Denosumab for Aneurysmal Bone Cysts of the Spine in an Australian Tertiary Paediatric Centre.

Aneurysmal bone cysts (ABC) are rare osteolytic, benign but often locally aggressive tumours of the long bones or vertebrae. For spinal ABC, surgical management, embolisation or sclerotherapy alone often carry high morbidity and/or high recurrence rates. Interruption of receptor activator of nuclear factor-kappa B ligand (RANKL) signalling holds promise as an effective therapeutic strategy for these tumours. We aimed to review the approach to surgical management and evaluate the efficacy and safety of denosumab for ABC of the spine in children. Retrospective review of 7 patients treated with denosumab using a standardised protocol for ABC of the spine in a tertiary paediatric centre. Surgical intervention was only conducted if there was spinal instability or significant neurological impairment. Denosumab 70 mg/m2 was given 4-weekly for at least 6 months, followed by 2 doses of zoledronate 0.025 mg/kg, aiming to prevent rebound hypercalcaemia. All patients achieved stability of the spine and resolution of neurological impairment, if present. Six patients achieved metabolic remission and have ceased denosumab without recurrence to date; the other showed clinical and radiological improvement without complete metabolic remission. Three patients developed symptomatic hypercalcaemia 5-7 months after cessation of denosumab, requiring additional bisphosphonate treatment. We present our algorithm for the surgical and medical management of paediatric spinal ABC. Denosumab produced a radiological and metabolic response in all patients, with complete remission in most. Follow-up time was not long enough to evaluate the endurance of response after cessation in some patients. Incidence of rebound hypercalcaemia in this paediatric cohort was high, prompting a change to our protocol.

The role of neoadjuvant denosumab in the treatment of aneurysmal bone cysts: a case series and review of the literature.

OBJECTIVE: Aneurysmal bone cysts (ABCs) are benign cystic lesions most commonly occurring in the long bones of pediatric patients. Spinal ABCs may be difficult to resect given their invasive, locally destructive nature, proximity to critical structures such as the spinal cord, and their intrinsic hypervascularity, for which complete embolization is often constrained by radiculomedullary segmental feeders. Denosumab, a monoclonal antibody that binds the receptor activator of nuclear factor kappa B (NF-κB) ligand, has been utilized in the treatment of ABCs most often as a rescue therapy for recurrent disease. Here, the authors present 3 cases of neoadjuvant denosumab use in surgically unresectable tumors to calcify and devascularize the lesions, allowing for safer, more complete resection. METHODS: This is a single-center, retrospective case series treated at a tertiary care cancer center. The authors present 3 cases of spinal ABC treated with neoadjuvant denosumab. RESULTS: All 3 patients experienced calcification, size reduction, and a significant decrease in the vascularity of their ABCs on denosumab therapy. None of the patients developed new neurological deficits while on denosumab. Subsequently, all underwent resection. One patient continued denosumab during the immediate postoperative period because a subtotal resection had been performed, with stabilization of the residual disease. No complications were associated with denosumab administration. CONCLUSIONS: The use of denosumab in unresectable ABCs can cause calcification and devascularization, making safe resection more likely.

Percutaneous doxycycline sclerotherapy in a horse with a mandibular aneurysmal bone cyst.

OBJECTIVE: To describe the use and outcome of sclerotherapy with intralesional doxycycline foam in a horse with a mandibular aneurysmal bone cyst. STUDY DESIGN: Case report. ANIMALS: Client-owned 1 year old Standardbred filly. METHODS: The horse presented for progressive mandibular swelling. A 10 mg/mL doxycycline foam was prepared for intralesional injection. Three doses were injected into the lesion under computed tomographic guidance at 6 and 15 weeks after initial treatment. Volume reduction was monitored after each treatment with 3D volumetric rendering and region of interest segmentation using commercially available software. RESULTS: The volume of the lesion decreased from 458.7455 cm3 before treatment, to 363.3101 cm3 at 6 weeks, 273.5855 cm3 at 15 weeks, and 247.2316 cm3 6 months later, resulting in a total reduction of 54% of the initial volume. Bone formation was noted in the lesion. No adverse effects related to doxycycline foam injections were noted. The mandibular swelling was resolved after treatment. CONCLUSION: Intralesional doxycycline sclerotherapy was shown to be efficacious in reducing the volume of the aneurysmal bone cyst in the horse presented in this report. There was complete resolution of mandibular swelling with no side effects related to the intralesional injections.

Uso de denosumab en quiste óseo aneurismático: revisión de la literatura / Use of denosumab in aneurysmatic bone cyst: literature review

INTRODUCCIÓN Los quistes óseos aneurismáticos (QOAs) son tumores benignos, localmente agresivos, y con importante potencial de recidiva, que representan aproximadamente el 1% de todos los tumores óseos. Se describen múltiples tratamientos, como: escisión intralesional, embolización arterial selectiva, inyección de agentes esclerosantes, y radiación. Estos tratamientos tienen una tasa variable de eficacia, ya que la recurrencia puede llegar al 20% y puede estar asociada a comorbidades graves como la pérda funcional de la extremidad. OBJETIVO Realizar una revisión integradora de la literatura sobre el uso de denosumab para el tratamiento de QOAs, describiendo el perfil epidemiológico, la dosis utilizada, y las complicaciones. MÉTODO Se recopilaron artículos publicados en los últimos cinco años en la base de datos PubMed. La información recogida de los casos reportados fue la edad, el sexo, la ubicación del tumor, la realización de cirugía antes y/o después del tratamiento con denosumab, la dosis utilizada, las complicaciones, y la recurrencia. RESULTADOS Se analizaron 7 artículos, 4 reportes de casos y 3 series de casos, escritos en inglés, y publicados de 2014 a 2019. La mayoría de los pacientes eran del sexo femenino, con una edad promedio de 14 años, y el tumor localizado en la columna. CONCLUSIÓN El uso de denosumab en el tratamiento de QOAs ha tenido una buena respuesta, ya que tiene bajas tasas de recurrencia y complicaciones; sin embargo, hacen falta más estudios para definir el protocolo de tratamiento.

INTRODUCTION Aneurysmal Bone Cysts (ABCs) are locally-aggressive benign tumors with relevant potential for recurrence, representing approximately 1% of all bone tumors. Multiple treatments are described for them, such as: intralesional excision, selective arterial embolization, injection of sclerosing agents, and radiation. These treatments have a variable efficacy rate, can reach 20% and may be associated with serious comorbidities such as functional loss of the limb. OBJETIVE To perform an integrative review of the literature on the use of denosumab in the treatment of ABCs, describing the epidemiological profile, the dosage used, and the complications. METHODOLOGY Articles published in the past five years were retrieved from the PubMed database. The information collected from the cases reported was age, gender, tumor location, the performance of surgery before and/or after the denosumab treatment, the dose used, the complications, and recurrence. RESULTS We analyzed 7 articles, 4 case reports and 3 case series, written in English, and published from 2014 to 2019. Most patients were female, with an average age of 14 years, with the tumor located in the spine. CONCLUSION The use of denosumab in the treatment of ABCs yielded good results, with low rates of recurrence and complications. However, further studies are needed to define a treatment protocol.

Aneurysmal bone cyst and osteoblastoma after neoadjuvant denosumab: histologic spectrum and potential diagnostic pitfalls.

The use of denosumab to treat giant cell tumors of bone (GCT) and other giant cell-containing bone tumors has become more common. While the clinicopathologic features of denosumab-treated giant cell tumors of bone have been well-illustrated, descriptions of other denosumab-treated bone tumors are very limited. Surgical pathology files of two institutions and consultation files from two authors were searched for denosumab-treated aneurysmal bone cysts and denosumab-treated osteoblastomas. Clinicopathologic features were reviewed and analyzed. We identified four patients with denosumab-treated bone tumors other than GCT from our surgical pathology and consultation files, including two aneurysmal bone cysts and two osteoblastomas. All were treated with denosumab for 0.5-7.0 (median 4.5) months. Radiologically, denosumab-treated tumors showed decreased size with increased ossification and mineralization on CT and heterogeneous intermediate to hypointense signal on MRI. Histologically, denosumab-treated aneurysmal bone cyst contained thin, elongated, curvilinear, and anastomosing strands of bone with empty lacunae, while denosumab-treated osteoblastoma showed circumscribed nodules of woven bone lined by small osteoblasts. Denosumab-treated aneurysmal bone cyst and osteoblastoma showed treatment-related morphologic changes that can mimic other bone neoplasms. Their recognition requires correlation with the clinical history of denosumab use and radiologic findings.

Denosumab in the management of Aneurysmal bone cyst.

BACKGROUND: Aneurysmal bone cyst (ABC) is a benign, locally aggressive tumour that arises predominantly in long bones and spine. Following the encouraging results of denosumab use in Giant Cell Tumors (GCT) and the histological similarities between ABC and GCT, the interest on the role of denosumab in the therapeutic arsenal of the most advanced ABC is growing. The purpose of this literature review is to investigate the current state of knowledge about the use of denosumab in ABCs. METHODS: A literature research was conducted through PUBMED, COCHRANE and GOOGLE SCHOLAR using the keywords "aneurysmal bone cyst" AND "denosumab". Seventeen articles were included. RESULTS: A total of 43 cases were reported in the literature. There were 23 males, 20 females. The mean age was 15,9±8,1 year. Pain relief and neurological improvement were rapid and sustained. Radiological assessment showed ossification and/or volume reduction in 36/39 patients. Eight patients (18,6%) presented a recurrence after or during denosumab therapy of whom 7 were adults. Adverse events occurred in 11 patients, 5 of them were admitted to the intensive care unit due to hypercalcemia. CONCLUSION: Denosumab use in non-surgical ABCs has shown a positive impact in pain and neurological symptoms. The oncological outcome remains unclear with a recurrence rate of 18,6% during/after denosumab therapy, mostly in adults. However, regarding the potential clinical benefits, its use might be discussed in the most advanced cases. Further research and clinical trials are mandatory to precise its belonging in the therapeutic arsenal.

Mechanisms of acute hypercalcemia in pediatric patients following the interruption of Denosumab.

PURPOSE: Denosumab is a fully human monoclonal anti-RANK-L antibody that is clinically used to counteract the bone loss induced by exacerbated osteoclast activity. Indeed, its binding to RANK-L prevents the interaction RANK-L/receptor RANK that is essential for osteoclastogenesis and bone resorbing activity. Although there are many medications available to treat bone loss diseases, including bisphosphonates, Denosumab is highly effective since it reduces the bone erosion. The use in pediatric patients is safe. However, some concerns are related to the interruption of the treatment. Indeed, in this study, we reported hypercalcemia in two pediatric patients and alterations of circulating osteoclast precursors. METHODS: Peripheral Blood Mononuclear Cells (PBMC) were isolated from two pediatric patients with hypercalcemia after Denosumab interruption and from 10 controls. Cytofluorimetric analysis and in vitro osteoclastogenesis experiments were performed. RESULTS: Increase of CD16-CD14+CD11b+ cells was revealed in PBMC from patients reflecting the enhanced in vitro osteoclastogenesis. CONCLUSION: Our data suggest that precautions must be taken when Denosumab therapy is interrupted and gradual decrease of dose and/or timing of treatment should be performed. To prevent the onset of hypercalcemia that could be in the discontinuation phase, cytofluorimetric analysis of PBMC should be performed to evaluate osteoclast precursors.

Mineral and Bone Consequences of High Dose Denosumab Therapy to Treat an Aneurysmal Bone Cyst, a Child Case Report.

Aneurysmal bone cysts (ABCs) are rare benign pseudotumoral bone lesions with potential aggressive behavior due to the extensive destruction of surrounding bone. Traditionally, these tumors were treated with open surgery, but there is more and more a shift to less invasive procedures. In particular, treatment for spinal ABCs is generally unsatisfactory due to the risk of morbidity, neurological impairment and recurrence, and there is a need for innovative therapies. Denosumab has been reported as a useful treatment in giant cell tumors of bone (GCTB), so its efficacy has been tested also in other fibro-osseus lesions affecting children and adolescents, such as spinal aneurysmal bone cysts. The pediatric literature is limited to case reports and small series, all of which highlight the efficacy of this treatment on lesions growth and associated bone pain. Some of these reports have already reported well known side effects associated with denosumab, such as hypocalcemia at the beginning of the treatment, and rebound hypercalcemia at the discontinuation. The latter seems to be more frequent in children and adolescents than in adults, probably due to the higher baseline bone turnover in children. In addition, the use of denosumab in young patients could affect both bone modeling and remodeling, even if the consequences on the growing skeleton have not been reported in detail. Here we describe the case of a spinal ABC diagnosed in an 8-year old young boy which was not accessible to surgery but responded favorably to denosumab. Our aim is to describe the rapid changes in mineral and bone homeostasis in this patient, that required advice from the experts of the European Reference Network (ERN) for rare bone and endocrine diseases.

Combined Transarterial Embolization and Percutaneous Sclerotherapy as Treatment for Refractory and Nonresectable Aneurysmal Bone Cysts.

PURPOSE: To evaluate the safety and effectiveness of combined transarterial embolization and percutaneous sclerotherapy in the treatment of refractory and nonresectable aneurysmal bone cysts (ABCs) as assessed by imaging and clinical outcomes. MATERIALS AND METHODS: This retrospective, single-center study included 16 consecutive patients (9 women and 7 men; median age, 17 years [range, 6-25 years]) who underwent combined transarterial embolization (using ethylene vinyl alcohol) and percutaneous sclerotherapy (using ethanol gel and polidocanol) for refractory and nonresectable ABCs. The median follow-up was 27.3 months (range, 6.7-47.5 months). Grade of mineralization (5-point Likert scale), grade of fluid-fluid levels (FFLs; 4-point Likert scale), and contrast-enhancing lesion volume were evaluated before and after treatment. The quality of life was determined before and after treatment using the Musculoskeletal Tumor Society (MSTS) score and the 36-Item Short Form Survey (SF-36) health questionnaire. RESULTS: A mean of 1.6 ± 0.7 transarterial embolizations and 3.2 ± 1.7 percutaneous sclerotherapies were performed. No adverse events were observed. All patients showed either partial or complete response; no patient showed ABC recurrence. The grade of mineralization (3.7 ± 0.7 after therapy vs 1.4 ± 0.5 at baseline; P < .0001) and grade of FFL (3.5 ± 0.8 after therapy vs 1.9 ± 0.6 at baseline; P < .0001) significantly improved after therapy compared with baseline. The mean contrast-enhancing lesion volume significantly decreased after treatment compared with baseline (45.9 mm³ ± 96.1 vs 156.0 mm³ ± 115.3, respectively; P = .0003). The MSTS scores (28.8 ± 1.8 after treatment vs 14.1 ± 8.6 at baseline; P < .0001) and SF-36 findings revealed a significant improvement in the quality of life after treatment compared with baseline, leaving most patients without relevant constraints. CONCLUSIONS: Combined transarterial embolization and percutaneous sclerotherapy is a minimally invasive, safe, and effective treatment option for refractory and nonresectable ABCs. Treatment fostered bone mineralization and significantly improved patients' quality of life.

Aneurysmal bone cysts in the spine, causing neurological compromise: safety and clinical efficacy of sclerotherapy utilizing sodium Tetradecyl sulfate foam.

OBJECTIVE: To assess the clinical efficacy, technical feasibility, and safety profile of percutaneous sclerotherapy utilizing sodium tetradecyl-sulfate foam (STS) as a first-line treatment strategy for aggressive spinal aneurysmal bone cysts (sABCs) presenting with neurological compromise. MATERIALS AND METHODS: Between July 2013 and September 2019, eight consecutive patients (5 males; 3 females; mean age 22±17, range 7-52) underwent fluoroscopic/CT-guided intraosseous sclerotherapy for sABCs. Pain and/or neurological compromise was the primary indications. Procedural data, complications, imaging, and clinical results were analyzed. RESULTS: Technical success was achieved in all cases. Mean procedure time was 25±15 min (range 6-167); 1 to 5 repeat treatment cycles (mean 3.7±1.2) utilizing a mean 2.6mls±1.3 (range 1-6) of agitated 3% STS, with a DLP mean dose of 158±91 mGy*cm (range 62-331) per procedure. One reported a minor complication (pain), but no significant complications. Two patients had persistent neurological deficit due to cord compression despite successful sclerotherapy, requiring surgical resection (and were thereby excluded from the final outcome analysis). The remaining six patients demonstrated a significant reduction in tumor volume (p = 0.028), pain (p = 0.027), and SINS (spinal instability neoplastic score) (p = 0.027) at up to 5 years of follow-up (mean 20 ± 16.7, range 7-51 months). CONCLUSION: Percutaneous sclerotherapy with STS is a minimally invasive, technically feasible, safe, and effective first-line treatment for primary sABCs causing pain and neurological compromise, alleviating the need for extensive surgery. It is most effective with three or more treatment cycles, in patients with higher SINS, pain scores, or tumor volumes at the initial presentation.

Denosumab Treatment for Giant Cell Tumors, Aneurysmal Bone Cysts, and Fibrous Dysplasia-Risks and Benefits.

PURPOSE OF REVIEW: This review summarizes current understanding of the role of denosumab, an inhibitor of receptor activator of nuclear kappa-B ligand (RANKL), in the management of 3 skeletal neoplasms: giant cell tumors, aneurysmal bone cysts, and fibrous dysplasia. RECENT FINDINGS: A growing body of literature supports denosumab use in giant cell tumors, a neoplasm in which RANKL plays a clear pathogenic role. Comparatively less data is available in aneurysmal bone cysts and fibrous dysplasia; however, the pathogenic similarity of these disorders to giant cell tumors, as well as encouraging preliminary data, suggests denosumab may be useful. Denosumab's inhibitory effects on bone turnover are fully reversible after drug discontinuation. This raises important unanswered questions for clinical management, including potential risks of tumor recurrence and bone turnover rebound. Denosumab is a promising potential treatment for skeletal neoplasms. However, its clinical use is impacted by ongoing safety concerns related to postdiscontinuation rebound, particularly in children. There is a critical need to understand denosumab treatment and discontinuation effects on tumor recurrence and to develop strategies for long-term treatment in patients who cannot be managed surgically.

Qualitative evaluation of MRI features in aneurysmal bone cysts after percutaneous sclerotherapy.

OBJECTIVE: To report MRI findings of changes seen in aneurysmal bone cysts after percutaneous sclerotherapy treatment. MATERIALS AND METHODS: After applying exclusion criteria, a total of 36 patients who had aneurysmal bone cysts and undergone percutaneous sclerotherapy were included in this study. The pre-treatment and post-treatment MRIs were reviewed and multiple pre-determined MRI findings were evaluated. The presence of each post-treatment finding, as well as the time for each finding to develop, was recorded. RESULTS: Early post-sclerotherapy changes include increased perilesional edema and enhancement, which appear on MRI on average 5.1 months after the initial sclerotherapy. This is followed by decreased cystic areas, which can be seen on average 5.9 months after the initial treatment. The presence of fibrosis, improved cortical integrity, and improving mass effect are later post-treatment changes and appear on MRI on average 9.7 months, 10.6 months, and 16.1 months after the initial sclerotherapy, respectively. CONCLUSION: The early and late post-sclerotherapy MR findings of aneurysmal bone cysts were reported in this study.

Manejo del quiste óseo aneurismático acetabular con doxiciclina intralesional: a propósito de un caso / Acetabular aneurysmal bone cyst treated with intralesional doxycycline: a case report

Los quistes óseos aneurismáticos (QOA) son tumores benignos, expansivos, osteolíticos y localmente agresivos que se localizan principalmente en la metáfisis de los huesos largos. Aparecen predominantemente en niños y adultos jóvenes. La eliminación del QOA mediante cirugía conlleva altas tasas de recurrencia por lo que se emplean otras técnicas no quirúrgicas como las inyecciones intralesionales con doxiciclina. Se presenta el caso clínico de un niño de 7 años diagnosticado de quiste óseo aneurismático acetabular que fue tratado exitosamente con una dosis de 200 mg de doxiciclina intralesional previa aspiración de las cavidades para despresurizarlas. El paciente mostró reducción de la lesión y mejoría clínica tras la intervención, sin manifestaciones de recurrencia tras 34 semanas de seguimiento. (AU)

Aneurysmal bone cysts (ABCs) are benign, expansile, osteolytic and locally aggressive tumors. Typically, ABCs arise in metaphysis of long bones. They often appear in children and young adults. Wide en bloc resection is associated with high recurrence rates. Other non-surgical treatment methods include intralesional injections of doxycycline. We present the case of a 7-year-old male with acetabular ABC who was successfully treated with 200 mg of intralesional doxycycline. During surgery, one needle was used for aspiration to lower the injection pressure. At 34 weeks follow up, we observed a lesion volume reduction and the patient presented an improvement of symptoms without recurrence. (AU)

Aneurysmal bone cyst inadvertently treated with chemotherapy-A series of three cases.

Aneurysmal bone cyst (ABC) is a benign locally aggressive tumor that occurs in childhood and early adulthood. Most relevant differential diagnoses are the telangiectatic osteosarcoma and the giant cell tumor. In the present case series chemotherapy following the EURAMOS or the Euro-Ewing 99 protocol was externally applied in three patients with the misdiagnosis of ABC as malignant bone tumor. In all three cases, a significant reduction of the volume of the ABC was achieved. This is the first report about the use of neoadjuvant chemotherapy in ABC. Chemotherapy reduces the size of an ABC and leads to progressive sclerosis.

Hypercalcaemia after treatment with denosumab in children: bisphosphonates as an option for therapy and prevention?

BACKGROUND: Pharmacologic options for treatment of osteolytic diseases especially in children are limited. Although not licensed for use, denosumab, a fully humanized antibody to RANKL, is used in children with good effects. Among others, one possible indication are giant cell tumors and aneurysmatic bone cysts. However, there are reports of severe hypercalcemia during weeks to months after termination of denosumab, that are rarely seen in adults. METHODS: We collected data of four patients, aged 6-17 years, who experienced severe hypercalcemia after completion of treatment with denosumab for unresectable giant cell tumors of bone or aneurysmal bone cysts and methods of their treatment. The detailed case information were described. RESULTS: One patient was treated with long-term, high-dose steroid therapy, leading to typical Cushing's syndrome. Another patient was restarted on denosumab repeatedly due to relapses of hypercalcemia after every stop. Finally, in two patients, hypercalcemia ceased definitely after treatment with bisphosphonates. However, several applications were necessary to stabilize calcium levels. CONCLUSIONS: There is a considerable risk of hypercalcemia as an adverse effect after denosumab treatment in children. Therapeutic and, preferably, preventive strategies are needed. Bisphosphonates seem to be an option for both, but effective proceedings still remain to be established.

Aneurysmal bone cyst: results of an off label treatment with Denosumab.

BACKGROUND: The treatment of aneurysmal bone cysts (ABCs) has evolved and less invasive methods have been tried. Denosumab is a monoclonal antibody which inhibits osteoclasts. It has been shown to be effective in giant cell tumour of bone (GCT) of bone and hence promises some effect also in ABC. We report on 6 patients treated with Denosumab and compare our results to the cases already published. METHODS: Data of 6 patients with ABCs and patients whose treatment included Denosumab were retrospectively analyzed. Denosumab was used at a dose of 120 mg on days 1, 8, 15 and 29, and every 4 weeks thereafter. In some of these patients the dose was reduced at the end of the treatment. Clinical and radiological responses were evaluated. RESULTS: In 4 female and 2 male patients with a mean age of 17 years (range: 6-30 years) the lesions were located in the sacrum (2), in distal radius, distal femur, talus and pelvis. One of the sacral lesions healed after 12 months and has stayed stable for 3 years since. The second patient received 2 years of therapy with recalcification, but recurred 1 year later and is under renewed therapy. The pelvic lesion improved but recurred. This patient has a 13-years history of intermittent therapy including surgery, two pregnancies and remains in a stable situation. The lesion of the talus did not improve with Denosumab after surgery and was complicated by destruction of the ankle joint with osteoarthritis. Recurrent lesions of the distal femur and the distal radius, previously treated by curettage and bone grafting healed under Denosumab and have remained stable for 2 and 3 years, respectively. One case of severe hypercalcemia was observed in a 7-year old child 6 months after discontinuation of Denosumab. CONCLUSION: Denosumab provides a treatment option for ABCs in anatomically critical locations. Adjuvant application might reduce the rate of local recurrence. In young patients, severe rebound hypercalcemia months after discontinuation of Denosumab may occur.