Circulating levels of midregional parathyroid hormone-related protein in hypercalcaemia of malignancy

Evaluation of Diagnostic Workup and Etiology of Hypercalcemia of Malignancy in a Cohort of 167 551 Patients Over 20 Years

Context

Hypercalcemia of malignancy (HCM) has not been studied in a fashion to determine all possible mechanisms of hypercalcemia in any given patient.

Objective

The 2 objectives were to assess the completeness of evaluation and to determine the distribution of etiologies of HCM in a contemporary cohort of patients.

Methods

A retrospective analysis was performed of patients with cancer who developed hypercalcemia over 20 years at a single health system. Laboratory data were electronically captured from medical records to identify cases of parathyroid hormone (PTH)-independent hypercalcemia. The records were then manually reviewed to confirm the diagnosis of HCM, document the extent of evaluation, and determine underlying etiology(ies) of HCM in each patient.

Results

The initial data set included 167 551 adult patients with malignancy, of which 11 589 developed hypercalcemia. Of these, only a quarter (25.4%) had assessment of PTH with a third of the latter (30.9%) indicating PTH-independent hypercalcemia. Of those with PTH-independent hypercalcemia, a third (31.6%) had assessment of PTH-related peptide (PTHrP) and/or 1,25-dihydroxy (1,25-OH) vitamin D and constituted the 153 cases of HCM examined in this study. Eighty-three of these patients had an incomplete evaluation of their HCM. The distribution of etiologies of HCM was therefore determined from the remaining 70 patients who had assessment of all 3 possible etiologies (PTHrP, 1,25-OH vitamin D, and skeletal imaging) and was as follows: PTHrP, 27%; osteolytic metastases, 50%; and 1,25-OH vitamin D, 39%, with combinations of etiologies being common (approximately 20%).

Conclusion

HCM is incompletely evaluated in many patients. The distribution of etiologies of HCM in this report differs significantly from the previous literature, warranting further study to determine whether its causes have indeed changed over time.

A case of neuroendocrine oncogenic osteomalacia associated with a PHEX and fibroblast growth factor-23 expressing sinusidal malignant schwannoma

Oncogenic osteomalacia is a rare paraneoplastic syndrome that is characterized biochemically by hypophosphatemia and low plasma 1,25-dihydroxyvitamin D3, and clinically by osteomalacia, pseudofractures, bone pain, fatigue, and muscle weakness. We present a patient with a malignant schwannoma as the underlying cause of this disorder. A permanent cell line (HMS-97) derived from this tumor showed evidence of neuroendocrine differentiation by immunohistochemistry and of neurosecretory activity by electron microscopy. The cell line did express PHEX (phosphate-regulating gene with homologies to endopeptidases located on the X-chromosome) and FGF-23 (fibroblast growth factor-23) transcripts on northern hybridization; however, none of the known mutations from the related mendelian disorders of X-linked hypophosphatemic rickets or autosomal-dominant hypophosphatemic rickets could be detected. Tumor cell (HMS-97)-derived conditioned medium did not inhibit phosphate transport in a standard opossum kidney cell assay and in animal experiments. The medium also showed no PTH1- or PTH2-receptor-stimulating bioactivity. HMS-97 cells might be useful for further studies that aim to determine the genetic mechanism that leads to the observed PHEX and FGF-23 expression, both of which might have a direct role in the pathogenesis of oncogenic osteomalacia. In addition, these cells might be a useful tool for the investigation of neuroendocrine Schwann cell function and autoimmune peripheral nerve disease.

The parathyroid hormone-related protein

Many physiologic roles of PTHrP are emerging. The protein functions locally in diverse tissues, often regulating the entry of cells into a differentiation pathway or acting as an epithelial signal in epithelial-mesenchymal interactions. To carry out these functions, PTHrP uses the receptor it shares with PTH or one of several PTHrP receptors that have evolved to recognize selectively the PTH-like region of PTHrP or other domains. Thus, PTHrP is a polyhormone. An exquisite selectivity barrier allows PTHrP to carry out its local tissue functions at the same time PTH uses their shared receptor to regulate systemic calcium homeostasis. This barrier is breached under pathologic circumstances, such as when malignant tumors secrete enough PTHrP into blood to cause PTH-like effects, including hypercalcemia. Powerful genetic models that have been developed in the past 7 years promise to give continuing insights into the physiology and pathophysiology of PTHrP.

Regulation of PTHrP and PTH/PTHrP receptor by extracellular Ca2+ concentration and hormones in the breast cancer cell line 8701-BC

It was previously reported that 8701-BC breast tumour cells express the gene for parathyroid hormone-related peptide (PTHrP) and PTH/PTHrP receptor (PTHrP-R) and release immunoreactive PTHrP (iPTHrP) into the extracellular medium. Since the regulation of PTHrP and PTHrP-R by breast cancer cells has been poorly investigated so far, we have chosen the 8701-BC cell line as a model system to investigate whether alterations in the extracellular Ca2+ concentration ([Ca2+]e) and treatment with some well-known differentiation agents for breast cells, such as dimethyl sulfoxide, hydrocortisone, progesterone, prolactin, all-trans retinoic acid and transforming growth factor-beta1 might (i) modulate quantitatively the release of iPTHrP, (ii) affect the PTHrP promoter usage and mRNA splicing patterns, and (iii) modify the expression of PTHrP-R. The data obtained indicate that 8701-BC cells are potentially able to utilise different start sites and mRNA splicing patterns for PTHrP transcription, and respond to variations of [Ca2+]e and to the addition of two hormones, hydrocortisone and progesterone, with modifications in the extracellular amount of iPTHrP. Moreover, expression of PTHrP-R is also modulated by changes of [Ca2+]e or treatment with hydrocortisone. This indicates that the 8701 -BC cell line is a suitable in vitro model for further studies on the complex molecular regulation of the PTHrP/PTHrP-R pair in breast cancer.

Concentration of insulin-like growth factor (IGF)-I and -II in iliac crest bone matrix from pre- and postmenopausal women: relationship to age, menopause, bone turnover, bone volume, and circulating IGFs

Insulin-like growth factor-I (IGF-I) and -II are important local regulators of bone metabolism, but their role as determinants of human bone mass is still unclear. In the present study, we analyzed the concentration of IGF-I and -II in the bone matrix of 533 human biopsies from the iliac crest that were obtained during surgery for early breast cancer. There was an inverse association of bone matrix IGF-I concentration with age that was unaffected by menopause. Bone matrix IGF-I was positively associated with histomorphometric and biochemical parameters of bone formation and bone resorption and with cancellous bone volume. Based on the estimates of the linear regression analysis, women with a bone matrix IGF-I concentration 2 SD above the mean had a 20% higher bone volume than women with a bone matrix IGF-I concentration 2 SD below the mean. In contrast, serum IGF-I was neither correlated with bone turnover nor with bone volume and was only weakly associated with bone matrix IGF-I when adjusted for the serum concentration of IGF binding protein-3. Bone matrix IGF-II was positively associated with the osteoblast surface, but in contrast to IGF-I, tended to be positively associated with age and was unrelated to cancellous bone volume. In summary, our study suggests the following. 1) The concentration of IGF-I in cancellous bone undergoes age-related decreases that are similar to those of circulating IGF-I. 2) Menopause has no effect on this age-related decline. 3) Physiological differences in bone matrix IGF-I are associated with differences in iliac crest cancellous bone volume. 4) Bone matrix IGF-I is a better predictor of cancellous bone volume than circulating IGF-I. 5) The role of IGF-II in human bone tissue is clearly distinct from that of IGF-I.

Concentration of transforming growth factor beta in human bone tissue: relationship to age, menopause, bone turnover, and bone volume

Transforming growth factor beta (TGF-beta) is thought to play an important role in bone metabolism, but its relationship to human bone turnover and bone mass has not been examined yet. In this study, we measured the concentration of TGF-beta in 811 samples of male and female bone from four representative sites of the human skeleton and in the supernatants of 72 short-term human bone marrow cultures from the iliac crest. The concentrations of TGF-beta1 and TGF-beta2 in the bone matrix were positively correlated with histomorphometric indices of bone resorption and bone formation and with serum levels of osteocalcin and bone-specific alkaline phosphatase. We also observed a positive association between the release of TGF-beta in the bone marrow cultures and serum osteocalcin. Changes in the rate of cancellous or cortical bone remodeling with age or menopause were accompanied by corresponding changes in skeletal TGF-beta. In contrast, there was no significant relationship between the concentration of TGF-beta and bone volume at any skeletal site. In conclusion, our study supports the hypothesis that TGF-beta plays an important role in human bone remodeling, but fails to demonstrate an association between the skeletal concentration of TGF-beta and human bone mass.

Increased parathyroid hormone-related peptide in patients with hypercalcemia associated with islet cell carcinoma

OBJECTIVE

To report the high prevalence of increased parathyroid hormone-related peptide (PTHrP) in patients with islet cell carcinoma and associated hypercalcemia.

DESIGN

We conducted a retrospective study of PTHrP levels in patients with hypercalcemia and eucalcemia associated with islet cell carcinoma and compared these findings with those in healthy subjects.

MATERIAL AND METHODS

Using a sensitive PTHrP immunochemiluminometric assay, we measured PTHrP levels in 17 patients with islet cell carcinoma and 110 healthy subjects. The differences between PTHrP levels in patients with normal and those with high serum calcium concentrations were analyzed statistically.

RESULTS

PTHrP levels were significantly higher (P < 0.01) in 10 patients with hypercalcemia and islet cell carcinoma (median, 14.0 pmol/L; range, undetectable to 40.1) than in 7 patients with eucalcemia and islet cell carcinoma (median, undetectable; range, undetectable to 1.3 pmol/L) or in the 110 healthy subjects (median, undetectable; range, undetectable to 4.2 pmol/L). The range of increased PTHrP levels in hypercalcemic islet cell carcinoma was 2 to 20 times the upper normal limit (2.0 pmol/L). Decreased PTHrP and serum calcium and increased parathyroid hormone levels were demonstrated in two patients after effective therapy. For all seven eucalcemic patients with islet cell carcinoma, PTHrP levels did not differ significantly from those in healthy subjects.

CONCLUSION

PTHrP levels are increased in a substantial proportion of patients with hypercalcemia and islet cell carcinoma and seem to decrease after treatment of the underlying tumor. Measurement of PTHrP levels may be useful for confirming the diagnosis of hypercalcemia associated with malignant disease and for monitoring of therapy.

Reversible metastatic pulmonary calcification in a patient with multiple myeloma

A-52-year-old patient presented with a 2-year history of multiple myeloma, recurrent episodes of hypercalcemia, and extensive bone involvement. She developed pulmonary infiltrates, initially misdiagnosed as interstitial pneumonia. High-resolution computed tomography and bone scintiscanning indicated pulmonary calcification, which was confirmed by a transbronchial biopsy. Cytostatic treatment of multiple myeloma in combination with repetitive i.v. administration of bisphosphonates over a period of 6 months led to a significant improvement of clinical symptoms. Regression of pulmonary infiltrates was demonstrated by chest radiograph and computed tomography. There are only a few reports on pulmonary calcification in patients with multiple myeloma; the condition was associated mostly with progressive disease, kidney failure, adult respiratory distress syndrome and bad prognosis. In our patient isolated calcification of the lungs without involvement of other organ systems was successfully treated. These findings suggest that interstitial pulmonary calcinosis in multiple myeloma can be reversed by normalization of serum calcium levels using bisphosphonates combined with cytostatic treatment.

Glucocorticoids decrease the production of parathyroid hormone-related protein in vitro but not in vivo in the Walker carcinosarcoma 256 rat model

In 50-90% of cases, humoral hypercalcemia of malignancy (HHM) is due to tumor secretion of parathyroid hormone-related protein (PTHrP). Glucocorticoids are sometimes used as calcium lowering agents and there are in vitro results showing that glucocorticoids diminish PTHrP production. In this study we tested whether the serum-calcium-lowering effect of glucocorticoids is due to decreased PTHrP production by the tumor. As an animal and cell culture model we used the Walker carcinosarcoma (WCS) 256, a rat mammary carcinoma cell line producing PTHrP. In vitro, dexamethasone caused a dose-dependent inhibition of PTHrP production, whereby already 1-5 nmol/L revealed a significant decrease by WCS 256 cells. In contrast to these in vitro results, in WCS 256 tumor-bearing rats, dexamethasone (4 mg/kg body weight on day 4, and 1 mg/kg body weight from day 5 until day 7 after WCS transplantation; circulating dexamethasone levels > 20 nmol/L) did not decrease PTHrP production, PTHrP secretion, serum calcium, or tumor weight in vivo. We conclude that, in this PTHrP-mediated model of humoral hypercalcemia of malignancy, glucocorticoids do not decrease PTHrP production and secretion in vivo and do not show a calcium-lowering effect.

Distribution and functions of parathyroid hormone-related protein in vertebrate cells

Parathyroid hormone-related protein (PTHrP) was isolated from tumors and identified as the agent of humoral hypercalcemia of malignancy (HHM) in 1987. Since then its gene structure in several mammalian and an avian species has been analyzed and its gene expression demonstrated in many adult and embryonic tissues derived from all three germ layers. The composition and structure of PTHrP peptide depends on both differential gene splicing and posttranslational processing, which result in a range of peptides of potentially diverse functions. This chapter describes the distribution of PTHrP in both normal and neoplastic adult and embryonic tissues. PTHrP is of fundamental importance to cell survival because the absence of the gene is fatal; this aspect of PTHrP function in cell physiology becomes overwhelmingly important in neoplasia. Intracrine or paracrine actions for PTHrP seem to be most likely in mammalian and avian physiology, but in fishes high circulating levels suggest classic endocrine functions as well. Much remains to be learned of the biology of this fascinating protein.

Parathyroid hormone-related peptide and 8701-BC breast cancer cell growth and invasion in vitro: evidence for growth-inhibiting and invasion-promoting effects

It has been previously reported that 8701-BC cells, derived from a primary carcinoma of the breast, constitutively express parathyroid hormone-related peptide (PTHrP) gene and that N-terminal PTHrP immunoreactivity can be found in cell medium. Here we have firstly measured immunoreactive PTHrP in 8701-BC cell medium using antibodies raised against midregion and C-terminal fragments, and also demonstrated the expression of PTH/PTHrP receptor by 8701-BC cells. Secondly, we have examined the role, if any, elicited by diverse PTHrP domains on 8701-BC cell proliferation, and invasive behaviour in vitro related to production of extracellular proteolytic enzymes. Our data show that PTHrP [1-34], and, to a minor extent, [67-86] and [107-139], are anti-mitogenic but 'invadogenic' for 8701-BC cells, and suggest that diverse enzymatic activities may contribute to cell invasion in response to different PTHrP fragments. In light of the present data on a chemoattractive role for PTHrP in vitro, we hypothesize that this protein might intervene in local control of the invasive process in breast carcinoma.

Effects of passive immunization against parathyroid hormone-related protein: PTHrP is the responsible factor in mediating hypercalcemia in the Walker carcinosarcoma 256 rat model

The Walker carcinosarcoma (WCS) 256 is a well-characterized rat model of humoral hypercalcemia of malignancy (HHM). We addressed the question of whether parathyroid hormone-related protein (PTHrP) is the factor responsible for mediating HHM in this model. WCS 256 cells were subcutaneously implanted in female rats. We examined the plasma at days 0, 2, 4, 6, and 8. The midregional PTHrP measured by radioimmunoassay (RIA) and the plasma calcium increased significantly. Measuring PTHrP by a two-site immunoradiometric assay (IRMA) showed comparable results. There was a strong positive correlation between plasma calcium and midregional PTHrP (r = 0.85, p < 0.0001). A strong positive correlation between tumor weight and both midregional PTHrP (r = 0.83, p < 0.0001) and plasma calcium (r = 0.87, p < 0.0001) was also found. After surgical removal of the tumor at day 5, both plasma calcium and plasma PTHrP levels fell to within the normal range. Ip administration of native polyclonal antiserum against PTHrP(53-84) led to a significant decrease of plasma calcium. Extracted WCS 256 tumor showed 5-fold increased levels of midregional PTHrP compared with liver. Immunohistochemistry and Western blot were positive for PTHrP. RNA from the WCS 256 tumor was positive for PTHrP whereas liver tissue RNA was negative. WCS 256 cells grown in vitro also secreted PTHrP into the medium. We conclude that PTHrP is synthesized and secreted by WCS 256 and that PTHrP is the factor responsible for mediating hypercalcemia in the WCS 256 rat model.

Expression and processing of parathyroid hormone-related protein in a pancreatic endocrine cell tumour associated with hypercalcaemia

We describe a patient with a neuroendocrine tumour of the pancreas associated with hypercalcaemia which was attributed to production of parathyroid hormone-related protein (PTHrP) by the tumour. Plasma PTHrP 1-86 was significantly raised, and fell following surgical resection of the tumour. PTHrP mRNA and peptide were identified in tumour tissue by in-situ hybridization and immunohistochemistry respectively. PTHrP was quantitated in an extract of tumour tissue by three region-specific immunoassays (PTHrP 1-34 45.2 pmol/g, PTHrP 37-67 81.7 pmol/g, PTHrP 1-86 27.3 pmol/g) and suggested the presence of excess of amino-terminal and mid-region immunoreactivity. On chromatography of the tumour extract the first peak eluted as 22 kDa and comprised approximately equimolar 1-34, 37-67 and 1-86 activities. The second and major peak of 16 kDa contained only 37-67 activity, while the third peak of 6 kDa contained only 1-34 activity. This suggested that the tumour contained a native or intact form of PTHrP together with two major subfragments containing 37-67 and 1-34 activity respectively. Thus chromatographic separation and quantitation of PTHrP by region-specific immunoassays have provided new information on in-vivo proteolytic processing by tumour tissue by indicating that a site of cleavage is located between residues 17 and 61. Our findings are compatible with cleavage at residue 37, a site previously indicated from in-vitro studies.

Significance of plasma PTH-rp in patients with hypercalcemia of malignancy treated with bisphosphonate

BACKGROUND

Hypercalcemia of malignancy (HM) is one of the commonest metabolic complications associated with cancer. Plasma parathyroid hormone-related peptide (PTH-rp) is known to cause hypercalcemia in the vast majority of patients with HM.

METHODS

Fifty-two patients with HM were treated with a single infusion of 60 mg of pamidronate (3-amino-1-hydroxypropylidene-1, 1-bisphosphonate). Serum calcium and plasma PTH-rp levels were measured at the basal and after pamidronate therapy.

RESULTS

Normocalcemia was achieved in 43 (i.e., 83%) of these patients within 3 to 5 days. Eighty-one percent had increased plasma PTH-rp levels. There was no difference in the percentages of patients who had elevated plasma PTH-rp levels compared with those of patients with metastatic bone disease and humoral HM. However, the latter group of patients had significantly higher circulatory PTH-rp levels (P < 0.01). The pretreatment calcium levels were not correlated with the calcium-lowering responses nor with plasma PTH-rp levels. However, there was a significant positive correlation between pretreatment plasma PTH-rp levels and the nadir serum calcium (P < 0.001) and a negative correlation with the changes in serum calcium levels (P < 0.001) after pamidronate therapy. No relationship existed between pretreatment calcium levels or PTH-rp levels with the extent or the severity of the metastatic bone disease. Patients who had the highest PTH-rp levels had the worst prognosis, poorest calcium-lowering effect, shortest duration of normocalcemia, and required higher doses and frequent infusions of pamidronate to maintain normocalcemia. The nonresponders to therapy had a significantly higher mean plasma PTH-rp level (> 75 pg/ml) than the responders (P < 0.01).

CONCLUSIONS

The plasma PTH-rp levels may help to predict the calcium-lowering effect of bisphosphonate and give an indication of the prognosis in patients with HM. They may allow identification of patients who need higher doses and increased frequency of administration of bisphosphonate, thereby expediting the normocalcemic response.

Argyrophil cell hyperplasia and a carcinoid tumour in the stomach of a patient with sporadic Zollinger-Ellison syndrome

In the rat, hypergastrinaemia induced by drug treatment with omeprazole or potent H2-receptor antagonists leads to the development of gastric enterochromaffin-like cell carcinoids. In man, gastric carcinoids induced by hypergastrinaemia have been described only in patients with chronic atrophic gastritis type A and in patients with the multiple endocrine neoplasia syndrome type 1. This patient with Zollinger-Ellison syndrome without gastric mucosal atrophy and without evidence of the multiple endocrine neoplasia syndrome developed an argyrophil gastric carcinoid tumour. This observation indicates that hypergastrinaemia in the sporadic Zollinger-Ellison-syndrome may induce gastric carcinoids.

In vitro stability of endogenous parathyroid hormone-related protein in blood and plasma

We describe a systematic comparison of the effects of anticoagulants, protease inhibitors and conditions of sample handling on the in vitro stability of endogenous parathyroid hormone-related protein (PTHrP) in blood from patients with hypercalcaemia of malignancy (HM). When blood was separated within 15 min of collection, PTHrP1-86 levels measured by two-site immunoradiometric assay in serum and heparinized plasma were significantly lower than in ethylenediaminetetraacetic acid (EDTA) plasma (P < 0.02). PTHrP was unstable in blood kept at 20 degrees C for 4 h and inclusion of protease inhibitors reduced, but failed to abolish, this instability. In blood collected in the presence of EDTA, inclusion of leupeptin either alone or in combination with pepstatin and aprotinin increased the mean half-time of disappearance from 3.9 to 10.1 and 11.2 h, respectively (P < 0.05). In contrast, when blood containing EDTA was separated within 15 min, PTHrP was stable in plasma at 20 degrees C for at least 4 h. As a result of the instability of PTHrP1-86 immunoreactivity in whole blood at ambient temperatures we advise that for our immunoradiometric assay (IRMA) blood collected in EDTA should be separated within 15 min, and the plasma frozen until assay.

Levels of parathyroid hormone-related protein in hypercalcemia of malignancy: comparison of midregional radioimmunoassay and two-site immunoradiometric assay

Overproduction of parathyroid hormone-related protein (PTHrP) is a major cause of hypercalcemia of malignancy in patients with solid tumors. We measured plasma levels of the protein by a radioimmunoassay (RIA) against PTHrP(53-84) and by an immunoradiometric assay (IRMA) against PTHrP (1-86). Of 16 affected patients 7 had elevated PTHrP levels in both assays and 4 had elevated levels in the RIA only. Median levels were about tenfold higher in these patients when measured by RIA (median of 34 versus 2.2 pmol/l). Measurements from both assays were, however, highly correlated with each other in this patient group (P < 0.01). PTHrP was not elevated in 10 normocalcemic patients with lung carcinoma. During long-term follow-up of a patient with a mesothelioma of the pleura, PTHrP levels measured with both assays decreased during chemotherapy in parallel with a normalization of serum calcium. In another hypercalcemic patient suffering from renal carcinoma, PTHrP measured by IRMA decreased by 40% within 12 h after nephrectomy, whereas PTHrP measured by RIA did not show a significant decline. Direct comparison of the assay results thus pointed to the existence of heterogeneity of circulating forms of PTHrP in plasma. In conclusion, both immunoassays detected elevated levels of PTHrP in a fraction of patients with hypercalcemia of malignancy and thus may be a tumor marker during treatment of malignancies.