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Advances in Treating Metastatic Bone Cancer |
Author's Affiliation: Academic Unit of Medical Oncology, Weston Park Hospital, Sheffield, United Kingdom
Requests for reprints: Robert Coleman, Academic Unit of Medical Oncology, Weston Park Hospital, Sheffield, United Kingdom. E-mail: r.e.coleman{at}sheffield.ac.uk
| Abstract |
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| Incidence of Bone Metastases |
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70% of patients dying of these cancers have evidence of metastatic bone disease (Table 1
; ref. 1). However, bone metastases may complicate a wide range of malignancies, resulting in considerable morbidity and complex demands on health care resources. Carcinomas of the thyroid, kidney, and bronchus also commonly give rise to bone metastases, with an incidence at postmortem examination of 30% to 40%. However, tumors of the gastrointestinal tract rarely (<10%) produce bone metastases.
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| Distribution of Bone Metastases |
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| Prognosis |
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The prognosis after the development of bone metastases in breast cancer is considerably better than that after a recurrence in visceral sites. For example, in a study by Coleman and Rubens (4) of patients whose cancers were diagnosed in the 1970s and 1980s and who were treated at a single institution, the median survival was 24 months in those patients with first recurrence in the skeleton compared with 3 months after first relapse in the liver (P < 0.00001).
Coexisting nonosseous metastatic disease is important in determining prognostic differences between patients with bone metastases from the same type of tumor. Additionally, for patients with advanced breast cancer and metastatic disease confined to the skeleton at first relapse, the probability of survival is influenced by the subsequent development of metastases at extraosseous sites. In a study of 367 patients with bone metastases from breast cancer, those who later developed extraosseous disease had a median survival of 1.6 years compared with 2.1 years for those with disease that remained clinically confined to the skeleton (Fig. 1 ; P < 0.001; ref. 7).
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| Skeletal Morbidity |
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In women with disease confined to the skeleton at first relapse, the median time to first skeletal complication was 11 months, compared with 20 months in women with bone and extraosseous disease and 56 months in women without bone metastases at diagnosis of first relapse. No significant differences occurred between the groups in the type of first skeletal complication. In a multivariate analysis, the most significant predictor of subsequent skeletal complications was the presence of bone metastases at diagnosis of metastatic breast cancer, regardless of other sites of metastatic disease.
A retrospective analysis of 859 patients who developed bone metastases from breast cancer at Guy's Hospital between 1975 and 1991 was done to identify factors that predict complications from skeletal disease (9). Four groups were defined according to the sites of disease at diagnosis of bone metastases: bone disease only (n = 243), bone and soft tissue disease (n = 268), bone and pleuropulmonary disease (n = 237), and bone and liver disease (n = 111). Survival from diagnosis of bone metastases was longest for patients with metastatic disease confined to the skeleton (median survival, 24 months; Fig. 2 ; P < 0.001) and was least for patients with concomitant bone and liver metastases (median survival, 5.5 months).
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Prostate cancer. Prostate cancer is the most prevalent nondermatologic cancer in males. At presentation,
10% of patients have bone metastases, and almost all patients who die of prostate cancer have skeletal involvement (10). The clinical course of patients with metastatic prostate cancer can be relatively long, and several prognostic factors have been identified, including performance status, tumor grade, hemoglobin, serum lactate dehydrogenase, prostate-specific antigen, and alkaline phosphatase (1113).
Several studies have attempted to correlate the extent of skeletal metastatic involvement with survival in patients with advanced prostate cancer. A staging system based on distribution of bone metastases according to bone scintigraphy (axial versus appendicular) showed a significant association with survival (14). A different system based on the number of lesions identified by bone scintigraphy was also predictive of survival (15). However, although both systems were able to discriminate between patients at the extremes of their respective scales, neither was particularly effective at discriminating between patients toward the center of the range.
A bone scan index has been developed to quantify the extent of skeletal involvement by tumor more accurately (16). It is based on the known proportional weights of each of the 158 bones derived from the so-called reference man, a standardized skeleton in which postmortem-based individual bone weights were reported for the average adult. The bones were considered individually and assigned a numerical score, representing the percentage involvement with tumor multiplied by the weight of the bone (derived from the reference man). In an analysis of outcomes according to the bone scan index in 191 patients with androgen-independent prostate cancer, patients with low, intermediate, or extensive skeletal involvement had median survivals of 18.3, 15.8, and 8.1 months, respectively (16).
Other tumors that affect bone. Many other solid tumors may affect the skeleton. However, a relatively underevaluated tumor, renal cell cancer has a particular propensity for the development of highly vascular bone metastases that cause severe morbidity (17). This, coupled with the high incidence of hypercalcemia in advanced renal cell cancer, makes the disease particularly relevant for the study of bone-specific treatments and management strategies.
In patients with multiple myeloma, the median survival time is 2 to 3 years, and several prognostic factors have been established (18). For example, the median survival time of patients with high levels of both C-reactive protein and ß2-microglobulin was 6 months compared with 54 months for patients with low serum levels of these markers (19). Other candidate markers for prognosis include neopterin, interleukin 6, plasma cell labeling index, and lactate dehydrogenase.
| Clinical Features |
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Pain. Bone metastases are the most common cause of cancer-related pain (21). The pathophysiologic mechanisms of pain in patients with bone metastases are poorly understood but probably include tumor-induced osteolysis, tumor production of growth factors and cytokines, direct infiltration of nerves, stimulation of ion channels, and local tissue production of endothelins and nerve growth factors. Although
80% of patients with advanced breast cancer develop osteolytic bone metastases, approximately two thirds of such sites are painless (22).
Different sites of bone metastases are associated with distinct clinical pain syndromes. Common sites of metastatic involvement associated with pain are the base of skull (in association with cranial nerve palsies, neuralgias, and headache), vertebral metastases (producing neck and back pain with or without neurologic complications secondary to epidural extension), and pelvic and femoral lesions (producing pain in the back and lower limbs, often associated with mechanical instability and incident pain).
Hypercalcemia. Hypercalcemia most often occurs in those patients with squamous cell lung cancer, breast and kidney cancers, and certain hematologic malignancies (in particular myeloma and lymphoma). In most cases, hypercalcemia is a result of bone destruction, and osteolytic metastases are present in 80% of cases. In breast cancer, an association exists between hypercalcemia and the presence of liver metastases (23). This association may reflect a relationship between liver involvement and production or reduced metabolism of humoral factors with effects on bone such as parathyroid hormonerelated peptide or receptor activator of nuclear factor-
B ligand.
Secretion of humoral and paracrine factors by tumor cells stimulates osteoclast activity and proliferation, and there is a marked increase in markers of bone turnover (24). Several studies have established the role of parathyroid hormonerelated peptide in most cases of malignant hypercalcemia (25). The levels of circulating parathyroid hormonerelated peptide are elevated in two thirds of patients with bone metastases and hypercalcemia and in almost all patients with humoral hypercalcemia. The kidney also has a role in malignant hypercalcemia; as a result of volume depletion and the action of parathyroid hormonerelated peptide, renal tubular reabsorption of calcium is increased, further increasing serum calcium levels.
The signs and symptoms of hypercalcemia are nonspecific, and the clinician should have a high index of suspicion. Common symptoms include fatigue, anorexia, and constipation. If untreated, a progressive increase in serum calcium level results in deterioration of renal function and mental status. Death ultimately results from renal failure and cardiac arrhythmias.
Pathologic fractures. The destruction of bone by metastatic disease reduces its load-bearing capabilities and results initially in microfractures, which cause pain. Subsequently, fractures occur (most commonly in ribs and vertebrae). It is the fracture of a long bone or the epidural extension of tumor into the spine that causes the most disability. As the development of a long-bone fracture has such detrimental effects on quality of life in patients with advanced cancer, efforts have been made to predict sites of fracture and to preempt the occurrence of a fracture by prophylactic surgery.
Fractures are common through lytic lesions in weight-bearing bones. Damage to both cortical and trabecular bone is structurally important. Several radiological features have been identified that may predict imminent fracture; fracture is likely if lesions are large, are predominantly lytic, and erode the cortex. A scoring system has been proposed by Mirels based on the site, nature, size, and symptoms from a metastatic deposit (26). Using this system, lesions that scored >7 generally require surgical intervention; deposits that scored
10 had an estimated risk of fracture of >50%. More sophisticated predictive tools based on computed tomography of sites at risk of fracture are currently under evaluation.
Compression of the spinal cord or cauda equina. Spinal cord compression is a medical emergency, and suspected cases require urgent evaluation and treatment. Pain occurs in most patients, is localized to the area overlying the tumor, and often worsens with activities that increase intradural pressure (e.g., coughing, sneezing, or straining). The pain is usually worse at night, which is the opposite pattern of pain from degenerative disease. There may also be radicular pain radiating down a limb or around the chest or upper abdomen. Local pain usually precedes radicular pain and may predate the appearance of other neurologic signs by weeks or months. Most patients with spinal cord compression will have weakness or paralysis. Late sensory changes include numbness and anesthesia distal to the level of involvement. Urinary retention, incontinence, and impotence are usually late manifestations of cord compression. However, lesions at the level of the conus medullaris can present with early autonomic dysfunction of the bladder, rectum, and genitalia.
In a retrospective analysis of 70 patients with spinal cord compression secondary to breast cancer, the most frequent symptom was motor weakness (96%) followed by pain (94%), sensory disturbance (79%), and sphincter disturbance (61%; ref. 27). Ninety-one percent of patients had at least one symptom for >1 week; 96% of those ambulant before therapy maintained the ability to walk. In those unable to walk, 45% regained ambulation, with radiotherapy and surgery equally effective. Median survival was 4 months. The most important predictor of survival was the ability to walk after treatment. These results suggest that earlier diagnosis and intervention may improve both outcome and survival.
Spinal instability. Back pain is a frequent symptom in patients with advanced cancer and in 10% of cases is due to spinal instability. The pain, which can be severe, is mechanical in origin, and frequently the patient is only comfortable when lying still. Surgical stabilization is often required to relieve the pain, and although such major surgery is associated with considerable morbidity and mortality, excellent results can be obtained with appropriate patient selection.
| Use of Bone Biochemical Markers to Predict Skeletal Morbidity and Clinical Outcome |
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Recent studies indicate that the risk of skeletal complications in both breast and prostate cancer is strongly related to the rate of bone resorption (30, 31). Such events are uncommon when bone resorption is normal but become increasingly frequent as the bone resorption rate increases. The author's group published a report on the use of the bone resorption marker n-telopeptide of type 1 collagen (NTX) that suggested biochemical monitoring was useful in the identification of patients at high risk of skeletal complications. In this relatively short-term study of 121 patients with metastatic bone disease, monthly measurements of urinary NTX during treatment with a range of bisphosphonates were made (3). All skeletal-related events, plus hospital admissions for control of bone pain, and death during the period of observation were recorded. NTX was strongly correlated with the number of skeletal-related events and/or death (P < 0.001). Patients with NTX values above 100 nmol/mmol creatinine were many times more likely to experience a skeletal-related event and/or death than those with NTX values below this level (P < 0.01; Table 3 ).
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3,000) included in the phase 3 development program of zoledronic acid. In these studies, the relationships between the most recent bone marker measurement and outcome during the next 1 to 3 months were assessed. These analyses showed that elevated NTX levels were highly predictive of skeletal events, progression in bone, and death in both the absence (ref. 31; Table 4
) and presence (ref. 32; Table 5
) of bisphosphonate treatments. Similar relationships were seen between bone alkaline phosphatase, a bone formation marker (Table 5), and outcome, although NTX was the most predictive. These observations suggested that a more cost-effective use of bisphosphonates might be to delay starting treatment with bisphosphonates until patients have an NTX level above the reference range for a healthy young adult (<50 nmol/mmol creatinine).
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The rate of bone resorption varies both between patients and within patients during periods of disease remission and progression. Patients with normal or only minimally accelerated bone resorption probably do not need the intensity of treatment provided by current schedules of highly potent aminobisphosphonates. Additionally, clinical benefit from bisphosphonates seems to be related to the effective suppression of accelerated bone resorption. Evidence is increasing that the aim of bisphosphonate treatment in advanced cancer (32, 37), as it is in benign bone diseases (38), should be to normalize bone resorption. This suggests that a tailored approach to bisphosphonates therapy may be a more appropriate, safer, and cost-effective approach than the currently licensed and recommended fixed 3- to 4-week schedule of i.v. treatment. This hypothesis is being tested in a large National Cancer Research Institute supported phase 3 clinical trial in the United Kingdom (BISMARK, EudraCT no. 2005-001376-12).
| Open Discussion |
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Dr. Coleman: It's probably a surrogate marker for the tempo of the disease, wherever that disease may be. Interestingly, these markers are a better predictor of death than they are of skeletal complications. Most patients don't die directly of their bone disease; they die of their liver disease or wherever their disease is. Nevertheless, these markers are telling us that for whatever reason we're not achieving control of bone resorption and maybe with an alternative therapeutic approach we could improve on that.
Dr. Roodman: Looking at the trial of prostate cancer patients, for example, were bone resorption markers going up earlier or sooner than prostate-specific antigen, for example, in these patients? Can this be used as a surrogate for changing therapy rather than adding another bone resorption antagonist?
Dr. Smith: We've tried to address this question in a prostate cancer study. One of the ways you might think about is whether these markers are a surrogate for volume of bone disease. We've done multivariate analyses trying to control for all the known published prognostic markers. In multivariate analyses, we found that higher levels of BAP but not NTx were independently associated with shorter survival after controlling for known prognostic variables.
Dr. Coleman: Are these updated analyses throughout the treatment?
Dr. Smith: We restricted the analyses to baseline variables to allow equal consideration of other variables and comparison to other prognostic models.
Dr. Coleman: In this data set, we don't have CA15-3, so we're limited to an analysis in prostate cancer, where obviously PSA was measured regularly. There is literature comparing bone markers and tumor markers for response assessment, and neither work very well. Probably bone markers are slightly better in breast cancer than tumor markers.
Dr. Body: When both types of markers are high, they are probably better predictors of survival. At early stages of the disease, tumor markers are probably better than bone markers, whether in breast or in prostate cancer.
Dr. Coleman: We are focusing on bone-specific treatments. What we've lacked until now is an indicator of what we're achieving in individual patients. All the trials are based on the effects on populations of patients, and yet none of us has a way of saying whether a bisphosphonate is going to benefit an individual patient.
Dr. Suva: Can you use the velocity of the increases in the bone markers as a way to track that for a particular patient?
Dr. Coleman: Maybe, but we haven't looked at that.
Dr. Vessella: In relation to the PSA question, were you asking if it was a good marker of early disease or prognostic? In our data, bone markers are more of an indication of the extent of the disease. When you have very early bone disease, PSA is clearly superior, because you have a background level of the bone markers, showing that in very early disease they seem to be normal. As the disease progresses in the bone, then they begin to increase. There's a correlation with bone burden, but not as an early diagnostic or prognostic marker of bone disease.
Dr. Coleman: I don't think there's any way that bone markers would be used as a diagnostic tool for bone metastases, because you can imagine the disruption caused by one small metastasis in the bone compared with the background of normal bone physiology and all the treatments we give would be overwhelmed.
| Footnotes |
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Received 4/14/06; accepted 6/20/06.
| References |
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M. Aapro, P. A. Abrahamsson, J. J. Body, R. E. Coleman, R. Colomer, L. Costa, L. Crino, L. Dirix, M. Gnant, J. Gralow, et al. Guidance on the use of bisphosphonates in solid tumours: recommendations of an international expert panel Ann. Onc., March 1, 2008; 19(3): 420 - 432. [Abstract] [Full Text] [PDF] |
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