Analgesic Treatment of Bone Metastases

Abstract

The presence of bone metastases predicts the presence of pain and is the most common cause of cancer-related pain. Although bone metastases do not involve vital organs, they may determine deleterious effects in patients with prolonged survival. Bone fractures, hypercalcaemia, neurologic deficits and reduced activity associated with bone metastases result in an overall compromise in the patient’s quality of life. A metastasis is a consequence of a cascade of events including a progressive growth at the primary site, vascularization phase, invasion, detachment, embolization, survival in the circulation, arrest at the site of a metastasis, extravasion, evasion of host defense and progressive growth. Once cancer cells establish in the bone, the normal process of bone turnover is disturbed. The different mechanisms responsible for osteoclast activation correspond to typical radiologic features showing lytic, sclerotic or mixed metastases, according to the primary tumour. The release of chemical mediators, the increased pressure within the bone, microfractures, the stretching of periosteum, reactive muscle spasm, nerve root infiltration and compression of nerves by the collapse of vertebrae are the possible mechanisms of malignant bone pain. Pain is often disproportionate to the size or degree of bone involvement. The use of analgesics according to the WHO ladder is recommended. The difficulty with incident pain is not a lack of response to systemic opioids, but rather that the doses required to control the incidental pain produce unacceptable side effects at rest. Opioids should be carefully used to balance background analgesia and breakthrough pain. Once analgesic optimization is achieved there are several options to treat breakthrough pain, including opioids with a fast onset.