Serum osteocalcin (BGP) in tumor-associated hypercalcemia

Usefulness of Bone Formation Markers in Breast Cancer

The skeleton is the main site affected by metastases and breast cancer is the most frequent tumor to invade bone. The assessment of bone metastases is difficult and biochemical markers of bone formation (BFMs) could be a promising alternative. Although the essential role of osteoblasts in the metastatic process of bone destruction is now well established, little attention has been paid to BFMs. We conducted a Medline search for studies about BFMs in breast cancer. Our review allows us to conclude that BFMs have high specificity but low sensitivity for the diagnosis of bone metastases. The available biochemical markers cannot replace imaging techniques for the diagnosis of bone metastases. Several studies indicate that BFM serum levels reflect total tumor burden in the skeleton. BFM levels are higher in patients with blastic lesions compared to those with lytic lesions. Serial measurements of BFMs could be useful for the clinical assessment of response to antineoplastic treatment or to bisphosphonate therapy. Besides markers of bone resorption, biochemical markers of bone formation are a promising alternative for the assessment of metastatic bone disease, but large prospective studies are needed to address this important issue.

Clinical review 165: Markers of bone remodeling in metastatic bone disease

Many cancers have a strong propensity to spread to bone. The processes involved in cancer dissemination to bone are complex and variable, and the changes in bone metabolism, once bony metastases have occurred, are usually profound. This review surveys the usefulness of bone markers in the diagnosis and follow-up of patients with malignant bone disease. In patients with established bone metastases, most markers of bone remodeling are abnormal compared with healthy controls or cancer patients without bone lesions. Although bone markers may have a potential as diagnostic tools in cancer patients, the available data do not allow final conclusions regarding the accuracy and validity of any of the presently used markers in the diagnosis of bone metastases. As regards monitoring of anticancer therapy, most markers of bone remodeling respond to active treatments. These indices therefore may have the potential to be used in the monitoring of antitumor therapies. However, most if not all of the available evidence on the use of bone markers in monitoring anticancer therapy is observational, and it remains unclear whether they have any beneficial effects on overall outcome. The same is true for their prognostic value, although evidence suggests that suppressed levels of bone formation or high rates of bone resorption are independent predictors of poor survival.

Serum prolidase I activity and some bone metabolic markers in patients with breast cancer: in relation to menopausal status

OBJECTIVES

The purpose of this study was to investigate the diagnostic value of some osteoblastic/osteoclastic biochemical markers and serum prolidase I activity in breast cancer (BC).

DESIGN AND METHODS

Serum bone gla protein (BGP), prolidase I activity, urinary deoxypyridinoline (Dpy) and calcium excretions were measured, in metastatic and nonmetastatic BC patients, and in 52 healthy women.

RESULTS

In patients with metastases, bone turnover markers were found to be significantly higher than those in the control group and in patients without metastases. Serum prolidase activity in patients with and without metastases was also significantly higher than those in the control group, but there was no difference between the two patient groups.

CONCLUSIONS

Bone turnover has been suggested to be accelerated in BC patients with the more pronounced osteolytic activation, especially in metastatic state. Serum prolidase in premenopausal period appears to be valuable in discriminating cancer patients from controls. BGP and to a lesser degree of Dpy, may be useful markers for predicting the metastatic bone involvement, as well as for the more cost effective management of BC patients and monitoring the effects of antiresorptive therapy of malignant osteolysis before any metastasis could be detected by other invasive techniques.

Biochemical markers to survey bone turnover

Molecular markers of bone turnover have gained increasing relevance in the evaluation of patients with metabolic bone diseases. Their clinical applications include the assessment of future osteoporotic fracture risk, complementation of bone density measurements, diagnosis of certain metabolic osteopathies, therapeutic decision making, and monitoring of therapeutic efficacy and patient compliance. One should be aware, however, that the results from large epidemiologic or clinical trials are sometimes difficult to translate into the everyday clinical situation. The individual patient often has more than one disease that might affect either bone turnover or the handling of the parameters mentioned (or both). Analytic and biologic variability of bone markers can be significant and also needs to be considered when using these indices. In the scientific setting, conventional and new markers of bone turnover can help to elucidate formerly unknown mechanisms and pathways. Because the development of ever more specific and sensitive markers of bone metabolism is progressing rapidly, we are likely to witness new insights into the pathophysiology of bone diseases in the near future.

Association between histomorphometry and biochemical markers of bone turnover in a longitudinal rat model of parathyroid hormone-related peptide (PTHrP)-mediated tumor osteolysis

Advanced tumor osteopathy is characterized by abnormal bone turnover. Using a rat model of parathyroid hormone-related peptide (PTHrP)-mediated tumor osteolysis, the aim of the present study was to define the sequential changes in, and the association between, biochemical and histomorphometric indices of bone metabolism during the early stages of developing tumor osteopathy. Eight-month-old Wistar rats (n = 48) were subcutaneously inoculated with either 2 x 10(6) cells of the Walker carcinosarcoma 256, or saline on day 0, and treated with either saline or the bisphosphonate ibandronate until killing on day 8. Serum calcium (sCa), alkaline phosphatase (sTAP), and osteocalcin (sOC) and urinary calcium (uCa), deoxypyridinoline (uDPD), and pyridinoline (uPYD) were measured daily. In a second semilongitudinal experiment (n = 70), the number of osteoclasts and osteoblasts (N.Oc, N.Ob), trabecular bone volume (BV/TV), and osteoid volume (O.Ar) were assessed by histomorphometry. In untreated tumor-bearing animals, osteoclast numbers increased by 74% on day 3 (5.4 +/- 2.4 vs. 3.1 +/- 1.5/mm(2), p < 0.05), and trabecular bone volume fell by 24% on day 4 (12.5 +/- 2.0 vs. 15.8 +/- 1.2%, p < 0.05). Both time course and magnitude of these changes were closely reflected by an increase in uDPD (0.46 +/- 0.14 vs. 0. 31 +/- 0.15 nmol/12 h, p < 0.05) and uPYD on day 4 (1.44 +/- 0.25 vs. 1.03 +/- 0.3 nmol/12 h, p < 0.05), sCa (3.8 +/- 0.52 vs. 3.0 +/- 0. 13 mmol/L, p < 0.01), and uCa (0.13 +/- 0.08 vs. 0.03 +/- 0.01 mmol/12 h, p < 0.001) on day 6, and sTAP (254 +/- 127 vs. 120 +/- 40 U/L, p < 0.001) on day 7 (mean +/- SD), whereas sOC remained unchanged until day 8. When combining the results of the two experiments, a high correlation was found between the number of osteoclasts and the urinary excretion of PYD (r = 0.91) and DPD (r = 0.89). Treatment with ibandronate delayed hypercalcemia, abolished hypercalciuria, and accelerated bone resorption. We conclude that osteoclast activation is an early event in PTHrP-mediated osteolysis, which is closely reflected by the renal excretion of pyridinium cross-links of type I collagen. Therefore, specific biochemical markers of collagen breakdown may be useful as early indicators of developing tumor osteopathy.

Tumor-induced hypercalcemia in a patient with extensive soft tissue sarcoma: effects of bisphosphonate therapy and surgery

Tumor-induced hypercalcemia (TIH) is a frequent complication of advanced cancer, but it has been rarely reported in patients with sarcoma. We describe the case of a young female patient with TIH and with an extensive synoviosarcoma of the left lower limb destroying the bony structures. Hypercalcemia was severe (18.3 mg/dl) and accompanied by low serum Pi and suppressed parathyroid hormone (PTH) and 1,25(OH)2 vit D3 serum concentrations. Hypercalcemia was successfully treated with ibandronate, a new third-generation bisphosphonate, and radical surgery was performed when the patient was normocalcemic. Circulating levels of PTH-related protein (PTHrP) were elevated at 22.5 pmol/L (NI < 9). PTHrP levels did not change after successful therapy of TIH, in contrast with PTH, which increased sharply. PTHrP levels were normalized after radical surgery. Moreover, low serum Pi with reduced threshold for phosphate excretion and increased tubular calcium reabsorption supported the notion that PTHrP was indeed the essential mediator of paraneoplastic hypercalcemia in this case despite the extensive bone destruction.

Serum levels of the pyridinoline crosslinked carboxyterminal telopeptide of type I collagen (ICTP) and osteocalcin in rachitic children in Nigeria

OBJECTIVES

We measured the levels of the pyridinoline crosslinked carboxyterminal telopeptide of type I collagen (ICTP) and osteocalcin (OC) in the serum of 12 rachitic and 27 healthy Nigerian children, and compared the performance of these relatively new markers of bone metabolism with established laboratory parameters of skeletal disease.

DESIGN AND METHODS

Active rickets was diagnosed on the basis of clinical and biochemical criteria. Serum calcium and phosphorus concentration and alkaline phosphatase activity were determined using clinically accepted methods. Radioimmunoassay was performed to quantify parathyroid hormone, 1-,25-dihydroxyvitamin D, OC, and ICTP.

RESULTS

The rachitic children had statistically significant serum elevations of ICTP and osteocalcin as compared with age- and sex-matched controls. Serum levels of ICTP correlated with alkaline phosphate activity.

CONCLUSIONS

As a marker of abnormal bone metabolism, ICTP performs at least as well as alkaline phosphate. ICTP and OC are valuable additions to the growing repertoire of bone markers.

Serum YKL-40: a new potential marker of prognosis and location of metastases of patients with recurrent breast cancer

YKL-40 is a recently discovered glycoprotein which is related in amino acid sequence to the chitinase protein family, but has no chitinase activity. Although the function of YKL-40 is presently unknown, the pattern of its expression by some tissues suggests that YKL-40 could function in tissue remodelling. The diagnostic features and relation to survival of serum YKL-40 have not been examined previously in human malignancies. In the present study YKL-40 was measured in serum obtained from 60 patients at the time that breast cancer recurrence was suspected. The median serum YKL-40 in patients with visceral or bone metastases was 328 and 157 micrograms/l, respectively and significantly higher compared to controls (99 micrograms/l, P < 0.001). Kaplan-Meier survival curves demonstrated that survival rates after 18 months were 24% for patients with high serum YKL-40 (> 207 micrograms/l = the 95 percentile of controls) and 60% for patients with normal serum YKL-40. The significance of the difference between the shorter survival of patients with high serum YKL-40 and the longer survival of patients with normal serum YKL-40 was high (P < 0.0009). When evaluated with other prognostic factors of survival after recurrence of breast cancer, serum YKL-40 and serum lactate dehydrogenase (LDH) were the most significant independent factors. The results indicate that determination of serum YKL-40 can be used as a prognostic marker related to the extent of disease and survival of patients with recurrence of breast cancer. In addition, the serum YKL-40 level may be of value in the follow-up of patients with breast cancer and in evaluating potential metastatic spread.

Circulating concentrations of interleukin-6 in cancer patients and their pathogenic role in tumor-induced hypercalcemia

Circulating interleukin-6 (IL-6) concentrations correlate with disease activity in severe inflammatory conditions, in sepsis and in some hematological malignancies. On the other hand, IL-6 is a potent stimulator of osteoclastogenesis and has been implicated as a contributory factor in the genesis of osteopenic conditions. We measured circulating IL-6 levels by a sensitive (detection limit of 10 U/ml) and specific bioassay in 103 patients with advanced cancer, including 41 with tumor-induced hypercalcemia before any specific hypocalcemic therapy. We related IL-6 concentrations to clinical features and to biochemical parameters of bone metabolism, including blood Ca, Ca2+, Pi, intact parathyroid hormone, parathyroid hormone-related protein, osteocalcin, 1,25-(OH)2-vitamin D and, as markers of bone resorption, the fasting urinary excretion of calcium (Ca/creatinine) and hydroxyproline. IL-6 levels were increased, i.e. detectable, in 23% of the patients, 8/41 (20%) hypercalcemic and 16/62 (26%) normocalcemic patients (NS); the distribution of the values was similar in the two groups. The presence of increased IL-6 concentrations was not related to any clinical characteristic, notably not to the survival nor to the existence of bone metastases, whether in hypercalcemic or normocalcemic patients; e.g., only 3/12 (25%) hypercalcemic subjects without bone metastases had elevated IL-6 levels. We found no significant correlations between IL-6 concentrations and any of the biochemical parameters studied. Hypercalcemic subjects with increased IL-6 had higher urinary Ca/creatinine levels than patients with normal IL-6 levels (P < 0.005) but this was not the case in normocalcemic subjects. Mean concentrations of inflammatory or other bone metabolism markers were not significantly different between patients with normal or with elevated IL-6 levels. In summary, circulating IL-6 levels were increased in 23% of 103 patients with advanced cancer, but the frequency of increased IL-6 concentrations was not related to the presence of hypercalcemia or to any marker of calcium metabolism or bone turnover. The pathogenic importance of circulating IL-6 in patients with solid tumors remains to be demonstrated and our data indicate that increased circulating levels of IL-6, possibly reflecting the activation of the immune system, only contribute in a minor way to the osteolytic process in patients with tumor-induced hypercalcemia.

Monitoring skeletal cancer metastases with the bone isoenzyme of tissue unspecific alkaline phosphatase

The efficacy of bone alkaline phosphatase (ALP) isoenzyme measurement using lectin precipitation in confirming metastatic bone lesions was compared with total ALP and osteocalcin assay in serum. Sixty-five patients with cancer and metastases to bone (n = 44), liver (n = 15) or lymph nodes (n = 6) as well as 33 healthy adults were studied. Assay of bone ALP is as sensitive but more specific than assay of total ALP in the identification of bone metastases. On the other hand, bone ALP did not correlate with osteocalcin, as is the case in other bone diseases. In the serial monitoring of nine patients with skeletal metastases, bone ALP correlated well with the presence of pain and the progression or regression of metastatic spread.

Associations and dissociations between serum bone Gla protein and alkaline phosphatase in skeletal metabolism

Serum bone Gla protein (BGP) and alkaline phosphatase (AP) activity were compared for the assessment of skeletal status in 11 normal pregnant women, 12 normal women on days 3 and 13 of the menstrual cycle, five postmenopausal women before and after 1 month of treatment with ethinyl estradiol (20 micrograms/day), five patients with cancer and hypercalcemia during treatment with calcitonin, and one patient with Paget disease during treatment with Plicamycin. BGP and AP correlated with each other only in the pregnant women. In all other circumstances, there was no correlation between these two serum osteoblast products. Furthermore, there were conditions in which the two measurements became discordant. These studies demonstrate that BGP and AP commonly are dissociated when used as measurements of skeletal status. Although both are osteoblast products, BGP and AP probably reflect different aspects of osteoblast differentiation and function.

The diagnostic and prognostic value of serum bone Gla protein (osteocalcin) in patients with recurrent breast cancer

Serum bone Gla protein (S-BGP), a marker of bone metabolism, was measured in 60 patients included in a staging programme for recurrent breast cancer. Other diagnostic procedures comprised S-alkaline phosphatase (S-AP), bone scan (B-scan), bilateral iliac crest bone marrow biopsies, and radiological bone survey. The sites of recurrence were bone (61%), bone marrow (46%), soft tissue (52%), lung (13%), pleura (11%), liver (4%), and brain (2%). Radiology and bone biopsy served as key diagnoses as to the presence or absence of bone metastases. The diagnostic efficiency of B-scan and S-AP was greater than that of S-BGP, and the result of BGP measurement was associated with neither extent nor number of bone metastases. However, the BGP values were significantly lower in patients who had visceral metastases, and the median duration of survival after recurrence was 13 months for patients with low S-BGP levels (= < 2.0 nmol l-1), compared to 18 months for patients with medium S-BGP values (2.0-2.9 nmol l-1), and 25 months for patients with high values (> 3.0 nmol l-1) (p = 0.19). Analyses of the simultaneous effect of univariate prognostic factors were performed using the Cox proportional hazards model. S-alkaline phosphatase (S-AP) and S-BGP were the only significant, independent prognostic factors.

Efficacy and safety of the bisphosphonate tiludronate for the treatment of tumor-associated hypercalcemia

Tiludronate is a new bisphosphonate whose efficacy has already been reported for the prevention of postmenopausal bone loss. We have evaluated its efficacy and tolerance by a dose-finding study in 19 hypercalcemic cancer patients after adequate intravenous (iv) rehydration. Treatment consisted of 3 days of iv tiludronate given at doses of 3.0 mg/kg/day (n = 3), 4.5 mg/kg/day (n = 3), or 6.0 mg/kg/day (n = 13); this iv therapy was followed by 17 days of oral tiludronate, 400 mg (n = 13) or 800 mg (n = 6) daily. Treatment had to be discontinued in 9 patients, including 3 because of evident treatment failure and 1 because of severe toxicity. After iv tiludronate, 13/18 patients had a normal Ca level, including 10/12 who had received 6.0 mg/kg/day, but Ca2+ levels were fully normalized in only 4/18 and 3/12 patients, respectively. After 6.0 mg/kg/day, Ca levels had fallen from 12.1 +/- 0.3 to 10.0 +/- 0.4 mg/dl (P less than 0.0005), whereas fasting urinary calcium excretion went from 0.639 +/- 0.099 to 0.272 +/- 0.054 mg Ca/mg creatinine on d4 (P less than 0.001). On the other hand, oral tiludronate was unable to normalize Ca in patients who were still hypercalcemic after the iv course, although the daily administration of 800 mg appeared to be more efficient than the 400 mg daily dosage. The administration of tiludronate caused an increase in serum phosphate levels, from 2.9 +/- 0.2 to 3.7 +/- 0.2 mg/dl after the iv course, probably through an increase in the TmP/GFR index, which went from 2.3 +/- 0.2 to 3.6 +/- 0.4 mg/dl (P less than 0.05). Three patients had an increase in serum creatinine levels after the iv course, one obese patient developing an acute renal insufficiency; during oral tiludronate therapy, 5 other patients also presented an increase in serum creatinine levels. Oral tiludronate administration was also associated with occasional nausea and vomiting. In summary, compared with aminobisphosphonates, tiludronate is not indicated for the treatment of tumor-associated hypercalcemia because of the need for high iv doses which are potentially nephrotoxic.

Plasma osteocalcin values and related hormonal parameters in patients subjected to a variety of prostate anticancer agents

Circulating osteocalcin (OC) and cortisol levels were measured in blood samples from 93 patients with dissaminated prostate cancer. Among these subjects 79 had not responded to therapy, while 14 had responded to a variety of anticancer treatment strategies (orchiectomy, cyproterone acetate (CPA), flutamide, Buserelin, diethylstilbestrol (DES), Estracyt, and polyestradiol phosphate). The control group consisted of 19 patients with benign prostatic hypertrophy. In the majority of these patients blood adrenocorticotropic hormone (ACTH), estradiol human growth hormone (hGH), and thyroid stimulating hormone (TSH) levels were also assessed. In nonresponders to therapy with DES and Estracyt subnormal circulating OC levels were measured, while normal OC values were found in nonresponders to other treatment strategies. In patient given Estracyt highly elevated estradiol levels were recorded. Subnormal and/or low-normal estradiol concentrations were found in patients subjected to CPA and DES. Elevated blood cortisol levels were assessed in subjects treated with DES and Estracyt while at the same time either subnormal and low-normal plasma ACTH concentrations were measured in these same patients. Accordingly, the decline observed in OC concentration seems to be a consequence of the well-established inhibitory effect of glucorticoids on osteoblast activity. The decline in blood cortisol levels obtained after administration of dexamethasone in patients given DES and Estracyt may be attributed both to possible changes in catabolic pathways and to the contribution of the negative neuroendocrinological feedback.

Osteocalcin: diagnostic methods and clinical applications

Osteocalcin is a small (Mr 5800), very interesting bone specific protein, synthesized by osteoblasts and measured in plasma as a biochemical indicator of bone formation. Many immunoassays for osteocalcin have been developed, including radio- and enzymoimmunoassays, with the use of monoclonal and polyclonal antibodies. These are used in many different clinical settings, including bone, kidney, and liver diseases. However, there is a wide range of published values for plasma osteocalcin concentrations in control and patient samples and this has hindered a more widespread adoption of osteocalcin measurement by clinicians. This review discusses how various immunoassays for osteocalcin may contribute to the wide variation of published values and suggests approaches for the development of standardized assays. For example, epitope specificity and immunoreactivity with multiple forms of osteocalcin and osteocalcin peptides in plasma are discussed. It also includes a recent update on interesting clinical applications of osteocalcin.

A short course of recombinant human growth hormone treatment stimulates osteoblasts and activates bone remodeling in normal human volunteers

The effects of recombinant human growth hormone (rhGH) on biochemical markers of bone turnover and bone mineral content (BMC) were investigated in 20 normal male volunteers (aged 22-31 years) randomized to treatment for 7 days with either rhGH (0.1 IU/kg subcutaneously twice a day) or placebo. Serum somatomedin C rose during treatment (p less than 0.001) but was not significantly different from baseline at day 14. The fasting urinary hydroxyproline/creatinine (p less than 0.001) and calcium/creatinine ratios (p less than 0.01) increased during treatment and remained elevated for 4 and 2 weeks, respectively. Serum bone gamma-carboxyglutamic acid-containing protein (BGP) increased during treatment (p less than 0.001) and remained elevated for 6 months (p less than 0.02). Serum bone alkaline phosphatase (B-AP), after an initial fall in the treatment period (p less than 0.001), increased slightly in the following months (p less than 0.01). In the rhGH group BMC was significantly higher than the prestudy value at day 14 (p less than 0.05) but was unaltered at the end of study. The simultaneous increase in markers of bone resorption and formation during rhGH treatment followed by a decline in resorption parameters within a few weeks and the prolonged effect on BGP and B-AP demonstrate that rhGH treatment stimulates osteoblasts and activates bone remodeling.

Aminohydroxypropylidene bisphosphonate (APD) treatment for tumor-associated hypercalcemia: a randomized comparison between a 3-day treatment and single 24-hour infusions

Intravenous aminohydroxypropylidene bisphosphonate (APD) normalizes serum calcium in most hypercalcemic cancer patients, however the optimal therapeutic scheme has not been established. We compared in a randomized prospective trial the efficacy and the tolerance of APD given as a 3-day treatment of daily 2-h infusions of 0.5 mg/k.d in 250 ml of saline (group A) with single 24-h infusions of 1.5 mg/kg (group B) or of 0.5 mg/kg in 1 liter of saline (group C). Thirty-three cancer patients remaining hypercalcemic after a 48-h rehydration period were included and monitored daily until normocalcemia or treatment failure was documented. Serum calcium became normal in all but 1 patient (in group C) but remained normal for only 1 or 2 days in 4 other patients (1 in A, 1 in B, 2 in C). The decline in total or ionized serum calcium was slightly less marked in group C than in the two other groups, but the differences were not significant. The fall of fasting urinary calcium excretion was however significantly less rapid in group C (p less than 0.05 from day 1 to day 4). Serum concentrations of iPTH and 1,25-dihydroxyvitamin D [1,25-(OH)2D] increased significantly in the three groups. Serum magnesium concentrations fell slightly from 1.41 +/- 0.05 to 1.28 +/- 0.04 mEq/liter (p less than 0.001) after rehydration but returned to normal after APD administration (day 5, 1.52 +/- 0.04 mEq/liter, p less than 0.001 versus day 0).(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term effects of Carbetimer on calcium and bone metabolism in man

Carbetimer is a new antineoplastic agent whose limiting toxicity consists of dose- and treatment duration-dependent hypercalcemia. We examined the short-term effects of Carbetimer on calcium metabolism on days, 1, 3 and 5 during 11 5-day courses (6.5-8.2 g/m2/day given over daily 2-h infusions, q 3-4 weeks). Blood parameters were measured before and after Carbetimer, whereas urinary parameters were studied in three consecutive 2-h collections before, during and after Carbetimer infusions. Carbetimer effects were similar regardless of the infusion day. We found a consistent decrease of plasma ionized Ca (Ca2+) levels from 4.56 +/- 0.05 mg/dl before infusion to 4.28 +/- 0.06 mg/dl after infusion (P less than 0.001) whereas total serum Ca (corrected for protein levels) did not change. The fall of Ca2+ stimulated parathyroid function, as suggested by the increased plasma PTH levels, the decreased serum phosphorus and TmP/GFR index, or the increased urinary phosphate and cyclic AMP excretion. Carbetimer infusions also induced a marked increase in urinary Ca excretion (expressed as mg Ca/mg creatinine) from 0.093 +/- 0.011 before to 0.359 +/- 0.042 during and 0.177 +/- 0.031 after infusion (P less than 0.011). These changes were best explained by Carbetimer-induced Ca chelation that we confirmed in vitro by incubating Carbetimer at various concentrations in whole blood for 2 h at 37 degrees C, e.g. 2 mg of Carbetimer/ml lowered Ca2+ from 4.82 to 3.20 mg/dl without changing total Ca levels. On the other hand, a direct effect of Carbetimer on bone cannot be excluded since we observed an increase of serum osteocalcin levels from 2.0 +/- 0.3 to 2.5 +/- 0.4 ng/ml after infusion (P less than 0.001). In summary, the short-term effects of Carbetimer on calcium metabolism markedly differ from the long-term effects. They mainly consist of a dose-related calcium chelation leading to a decrease in Ca2+ levels, an increase in urinary Ca excretion and a stimulation of parathyroid function.

Osteocalcin: a potential marker of metastatic bone disease and response to treatment

Serum osteocalcin (BGP) is an osteoblast product that probably reflects the rate of bone formation. It is a potential marker of skeletal metastases and, to investigate this, BGP was measured by radioimmunoassay in the serum of normal subjects and patients with breast or prostate cancer. Significantly higher levels were found in patients with metastatic bone disease in comparison to both normal subjects (P less than 0.001) and patients with non-metastatic cancer (P less than 0.05 for breast cancer and less than 0.001 for prostate cancer). The range of values was wide. Levels were higher in sclerotic than lytic bone metastases (P less than 0.01) and lower in patients with hypercalcaemia (P less than 0.001). Serial measurements of BGP were made in 53 patients with skeletal metastases from breast cancer receiving systemic therapy. At 1 month BGP rose by greater than 0.5 ng/ml in 15/16 responding patients compared with 7/23 patients with progressive disease (P less than 0.01). Responding patients also showed a rise in the bone isoenzyme of alkaline phosphatase and a paradoxical deterioration in the bone scan appearance, both reflecting a flare in osteoblast activity. The early increase in responding patients was followed by a gradual decrease over subsequent months as the osteoblast reaction induced by systemic therapy subsided. We conclude that BGP measurements reflect a wide variability of bone formation rates in metastatic bone disease. Bone formation was usually increased, particularly when metastases were sclerotic in appearance, but in patients with hypercalcaemia the low BGP levels suggest uncoupling of bone resorption and formation. Serial measurements of BGP may be useful in monitoring response to treatment.