US regulators have given the green light for Amgen's Xgeva in patients with a type of rare but not usually cancerous bone tumour.

The US Food and Drug Administration's decision means that Xgeva (denosumab) can now be used to treat adults and 'skeletally mature' adolescents with giant cell tumour of bone (GCTB) that cannot be adequately treated by surgery.

Approval was based on data from two open-label trials in 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%, and in the 47 patients whose tumours decreased in size, 51% had a duration of response lasting at least eight months, the firm said.

Common side effects observed in the clinical trial programme were joint pain, headache, nausea, fatigue, back pain and extremity pain, while the most common serious side effects being osteonecrosis of the jaw and inflammation or infection of the bone. 

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

Approval of Xgeva - which follows an accelerated review by the regulator - gives patients in the US access to the first and only treatment for the condition.

The drug was also cleared by the FDA for the prevention of skeletal-related events in patients with bone metastases from solid tumours in 2010, and is also marketed as Prolia for the prevention of fractures in postmenopausal women with osteoporosis.