The US Food and Drug Administration (FDA) has expanded the approved use of Amgen's Xgeva (denosumab) for the treatment of adults and skeletally mature adolescents with giant cell tumour of bone (GCTB) that is unresectable or where surgical resection is likely to result in severe morbidity. Xgeva was approved following a priority review by the FDA, a designation reserved for drugs that offer major advances in treatment, or provide a treatment where no adequate therapy exists.

GCTB typically affects individuals between the ages of 20 to 40. The disease is characterized by a bone destructive tumour that often results in fractures. When untreated, it often results in complete destruction of the affected bone, leading to bone fracture, joint dysfunction, deformity or amputation.

The approval of Xgeva is based on positive results from two open-label trials that enrolled patients with GCTB that was either recurrent, unresectable, or for which planned surgery was likely to result in severe morbidity. The overall objective response rate of the 187 patients evaluated was 25 per cent. The estimated median time to response was three months. In the 47 patients with an objective response, 51 per cent (24/47) had a duration of response lasting at least eight months. Three patients experienced disease progression following an objective response.

The safety profile of Xgeva in patients with GCTB was similar to that reported in studies of patients with bone metastases, and also appeared to be similar in skeletally mature adolescents and adults. Safety data was evaluated in 304 patients with GCTB who received at least one dose of Xgeva. Of these patients, 145 were treated for at least one year. The most common adverse reactions were arthralgia, headache, nausea, back pain, fatigue, and pain in the extremity. The most common serious adverse reactions were osteonecrosis of the jaw and osteomyelitis.

For patients with GCTB, Xgeva is administered as a subcutaneous injection (120 mg) every four weeks with additional 120 mg doses on days eight and 15 of the first month of therapy.

"With today's Xgeva FDA approval, Amgen can offer a much needed treatment option to patients who suffer from giant cell tumor of bone that cannot be adequately treated with surgery," said Sean E Harper, MD, executive vice president of Research and Development at Amgen. "Advances in our understanding of the underlying biology of this rare disorder have allowed Amgen to generate compelling clinical evidence to address the medical needs of patients and their healthcare providers."

XGEVA binds to RANK Ligand (RANKL), a protein essential for the formation, function and survival of osteoclasts - the cells responsible for bone resorption. Giant cell tumours of bone consist of stromal cells expressing RANKL and osteoclast-like giant cells expressing RANK receptor. Signaling through the RANK receptor contributes to osteolysis and tumour growth. XGEVA prevents RANKL from activating its receptor, RANK, on the surface of osteoclasts, their precursors and osteoclast-like giant cells.

GCTB is a locally aggressive, benign tumour afflicting younger adults between the ages 20 to 40. It is estimated that there are approximately 300-800 new cases of GCTB annually in the US. GCTB is unresectable in approximately 18-20 per cent of cases.

Most tumours occur in the long bones of the body, often around joints, but can also spread to the lungs in rare cases. Although giant cell tumors are slow growing, patients can experience severe bone pain, swelling, loss of mobility and pathologic fracture. Historically, there have been no approved therapies for GCTB. Surgery is the main treatment option for patients with resectable GCTB; however, surgery, such as amputation, may be associated with significant morbidity. These tumours also have a higher recurrence rate within the first three years of surgical intervention. When tumours recur, they become more difficult to treat and more likely to spread to other parts of the body.

Xgeva was approved by the US FDA for the prevention of skeletal-related events (SREs) in patients with bone metastases from solid tumours in 2010. XGEVA is not indicated for the prevention of SREs in patients with multiple myeloma. In clinical trials, XGEVA demonstrated a clinically meaningful improvement compared to the previous standard of care in preventing these bone complications.

In 2013, Xgeva was approved by the FDA as the first and only treatment for adults and skeletally mature adolescents with GCTB that is unresectable or where surgical resection is likely to result in severe morbidity.