Immunoreactive forms of circulating parathyroid hormone in primary and ectopic hyperparathyroidism

Bone Remodeling and Modeling: Cellular Targets for Antiresorptive and Anabolic Treatments, Including Approaches Through the Parathyroid Hormone (PTH)/PTH-Related Protein Pathway

Bone is continuously in a state of building and renewal, though the process of remodeling that takes place at many sites asynchronously throughout the skeleton, with bone formation and resorption equal at these sites (bone multicellular units). Remodeling takes place on bone surfaces, both on trabeculae and in the cortex, and serves the purposes of replacing old bone or that damaged by microfractures throughout the skeleton. The bone loss and consequent osteoporotic fractures that result from excess resorption over formation have mainly been prevented or treated by antiresorptive drugs that inhibit osteoclast formation and/or activity. Virtually all of the evidence leading to acceptance of antiresorptive drugs as treatment has depended upon their prevention of vertebral fractures. In recent decades, new prospects came of anabolic treatments that partly restore bone volume and microstructure restore bone that has been lost. The first of these was parathyroid hormone (PTH), shown by daily injection to increase markers of bone formation and prevent fractures. This field of interest enlarged with the discovery of PTH-related protein (PTHrP), so closely related in structure and action to PTH. The structural relationship between PTH and PTHrP is important in assessing their physiological and pharmacological roles, with the N-terminal domains of the 2 having virtually equal actions on target cells. Abaloparatide, a peptide analogue based on the structures of PTHrP and PTH, has been approved in some countries as a therapy for osteoporosis. Treatment through the PTH receptor activation pathway, and probably with any anabolic therapy, needs to be followed by antiresorptive treatment in order to maintain bone that has been restored. No matter how effective anabolic therapies for the skeleton become, it seems highly likely that there will be a continuing need for antiresorptive drugs.

Parathyroid hormone-related protein in breast cancer bone metastasis

Parathyroid hormone-related protein (PTHrP) was discovered as the tumor product causing the humoral hypercalcemia of malignancy. Its structural similarity to the hormone, PTH, with 8 of the first 13 amino acids identical, was sufficient to explain the sharing by PTHrP and PTH of a common receptor, PTH1R, although the remainder of the sequences are unique. PTHrP has important roles in development of several organs, including breast and bone, and functions as a paracrine factor postnatally in these and other tissues. In addition to its hormonal role in cancer, PTHrP is produced by two thirds of primary breast cancers and 90% of bone metastases from breast cancer, leading to the concept that its production in bone by breast cancer cells promotes bone resorption, thus favoring tumor establishment and expansion, and an exit from tumor dormancy in bone through downregulation of leukemia inducing factor receptor (LIFR). Cancer production of PTHrP is increased by bone-derived growth factors, with particular attention paid to TGFβ, as well as by promoter-driven transcriptional effects, such as the hedgehog signaling factor, GLI2, and microenvironment effects including changes in underlying stiffness of substrates for cells. Although interest has been focused on PTHrP-induced bone resorption in bone metastasis, a mechanistically separate, protective effect against tumor progression has been proposed. Although there is conflicting mouse data, there are clinical studies suggesting that increased production of PTHrP by breast cancers confers upon them a less invasive phenotype, an effect distinct from the bone resorption-stimulating action that favors bone metastasis.

Physiological and Pharmacological Roles of PTH and PTHrP in Bone Using Their Shared Receptor, PTH1R

Parathyroid hormone (PTH) and the paracrine factor, PTH-related protein (PTHrP), have preserved in evolution sufficient identities in their amino-terminal domains to share equivalent actions upon a common G protein-coupled receptor, PTH1R, that predominantly uses the cyclic adenosine monophosphate-protein kinase A signaling pathway. Such a relationship between a hormone and local factor poses questions about how their common receptor mediates pharmacological and physiological actions of the two. Mouse genetic studies show that PTHrP is essential for endochondral bone lengthening in the fetus and is essential for bone remodeling. In contrast, the main postnatal function of PTH is hormonal control of calcium homeostasis, with no evidence that PTHrP contributes. Pharmacologically, amino-terminal PTH and PTHrP peptides (teriparatide and abaloparatide) promote bone formation when administered by intermittent (daily) injection. This anabolic effect is remodeling-based with a lesser contribution from modeling. The apparent lesser potency of PTHrP than PTH peptides as skeletal anabolic agents could be explained by lesser bioavailability to PTH1R. By contrast, prolongation of PTH1R stimulation by excessive dosing or infusion, converts the response to a predominantly resorptive one by stimulating osteoclast formation. Physiologically, locally generated PTHrP is better equipped than the circulating hormone to regulate bone remodeling, which occurs asynchronously at widely distributed sites throughout the skeleton where it is needed to replace old or damaged bone. While it remains possible that PTH, circulating within a narrow concentration range, could contribute in some way to remodeling and modeling, its main physiological role is in regulating calcium homeostasis.

Multiple actions of parathyroid hormone-related protein in breast cancer bone metastasis

The sequence similarity within the amino-terminal regions of parathyroid hormone (PTH) and PTH-related protein (PTHrP) allows the two to share actions at a common site, the PTH1 receptor. A number of biological activities have been ascribed to actions of other domains within PTHrP. PTHrP production by late stage breast cancer has been shown to contribute to bone metastasis formation through promotion of osteoclast formation and bone resorption by action through PTH1 receptors. There is evidence also for a role for PTHrP early in breast cancer that is protective against tumour progression. No signalling pathway has been identified for this effect. PTHrP has also been identified as a factor promoting the emergence of breast cancer cells from dormancy in bone. In that case, PTHrP does not function through activation of PTH1 receptors, despite having very substantial effects on transcriptional activity of the breast cancer cells. This indicates actions of PTHrP that are non-canonical, that is, mediated through domains other than the amino-terminal. It is concluded that PTHrP has several distinct paracrine, autocrine, and intracrine actions in the course of breast cancer pathophysiology. Some are mediated through action at PTH1 receptors and others are controlled by other domains within PTHrP. LINKED ARTICLES: This article is part of a themed issue on The molecular pharmacology of bone and cancer-related bone diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.9/issuetoc.

Parathyroid Hormone-Related Protein, Its Regulation of Cartilage and Bone Development, and Role in Treating Bone Diseases

Although parathyroid hormone-related protein (PTHrP) was discovered as a cancer-derived hormone, it has been revealed as an important paracrine/autocrine regulator in many tissues, where its effects are context dependent. Thus its location and action in the vasculature explained decades-long observations that injection of PTH into animals rapidly lowered blood pressure by producing vasodilatation. Its roles have been specified in development and maturity in cartilage and bone as a crucial regulator of endochondral bone formation and bone remodeling, respectively. Although it shares actions with parathyroid hormone (PTH) through the use of their common receptor, PTHR1, PTHrP has other actions mediated by regions within the molecule beyond the amino-terminal sequence that resembles PTH, including the ability to promote placental transfer of calcium from mother to fetus. A striking feature of the physiology of PTHrP is that it possesses structural features that equip it to be transported in and out of the nucleus, and makes use of a specific nuclear import mechanism to do so. Evidence from mouse genetic experiments shows that PTHrP generated locally in bone is essential for normal bone remodeling. Whereas the main physiological function of PTH is the hormonal regulation of calcium metabolism, locally generated PTHrP is the important physiological mediator of bone remodeling postnatally. Thus the use of intermittent injection of PTH as an anabolic therapy for bone appears to be a pharmacological application of the physiological function of PTHrP. There is much current interest in the possibility of developing PTHrP analogs that might enhance the therapeutic anabolic effects.

Causes of discordant or negative ultrasound of parathyroid glands in treatment naïve patients with primary hyperparathyroidism

OBJECTIVES

To describe causes of discordant or negative parathyroid ultrasound and to assess factors influencing them.

MATERIALS AND METHODS

Retrospective review of patients who underwent parathyroidectomy between 2000 and 2012 was done. Imaging findings were compared with operative findings and pathology to identify discrepant (n=60; 32 negative, 28 incorrect) parathyroid ultrasounds.

RESULTS

Fifty (83.3%) patients had parathyroid adenoma, of which 10 (16.6%) were ectopic and three were double adenomas; 8 (13.3%) had multigland hyperplasia and two had parathyroid carcinoma. Discrepant reports were due to incorrect localisation in 8 (13.3%); difficulty in differentiating thyroid from parathyroid lesion in 12 (20%); large and small size in two and three patients, respectively; overcall in 5 (8.3%) and satisfaction of search in 7 (11.7%) patients. There was significant correlation between presence of multi-nodular goitre and incorrect reports (χ(2)=4.112, p=0.04). Experience of ultrasound operators performing initial and second look ultrasound was significantly different (p<0.0001). Second look ultrasound was concordant with surgical findings in 39(65%) patients; 21 (66%) patients with initially negative ultrasound and four out of five extra-mediastinal ectopic lesions. Ten patients with negative initial ultrasound had elongated parathyroid lesion. Scintigraphy was concordant in 44 (73.3%) patients and nine were ectopic.

CONCLUSION

Second look ultrasound performed by experienced operator for negative or discordant initial ultrasound of parathyroid is a useful strategy which will improve the accuracy of parathyroid ultrasound. Being able to differentiate thyroid from parathyroid lesion is a factor which will influence performance of parathyroid ultrasound.

Twenty-five years of PTHrP progress: from cancer hormone to multifunctional cytokine

Twenty-five years ago a "new" protein was identified from cancers that caused hypercalcemia. It was credited for its ability to mimic parathyroid hormone (PTH), and hence was termed parathyroid hormone-related protein (PTHrP). Today it is recognized for its widespread distribution, its endocrine, paracrine, and intracrine modes of action driving numerous physiologic and pathologic conditions, and its central role in organogenesis. The multiple biological activities within a complex molecule with paracrine modulation of adjacent target cells present boundless possibilities. The protein structure of PTHrP has been traced, dissected, and deleted comprehensively and conditionally, yet numerous questions lurk in its past that will carry into the future. Issues of the variable segments of the protein, including the enigmatic nuclear localization sequence, are only recently being clarified. Aspects of PTHrP production and action in the menacing condition of cancer are emerging as dichotomies that may represent intended temporal actions of PTHrP. Relative to PTH, the hormone regulating calcium homeostasis, PTHrP "controls the show" locally at the PTH/PTHrP receptor throughout the body. Great strides have been made in our understanding of PTHrP actions, yet years of exciting investigation and discovery are imminent. © 2012 American Society for Bone and Mineral Research.

Parathyroid hormone related protein (PTHrP) in tumor progression

Parathyroid hormone-related protein (PTHrP) is widely expressed in fetal and adult tissues and is a key regulator for cellular calcium transport and smooth muscle cell contractility, as well as a crucial control factor in cell proliferation, development and differentiation. PTHrP stimulates or inhibits apoptosis in an autocrine/paracrine and intracrine fashion, and is particularly important for hair follicle and bone development, mammary epithelial development and tooth eruption. PTHrP's dysregulated expression has traditionally been associated with oncogenic pathologies as the major causative agent of malignancy-associated hypercalcemia, but recent evidence revealed a driving role in skeletal metastasis progression. Here, we demonstrate that PTHrP is also closely involved in breast cancer initiation, growth and metastasis through mechanisms separate from its bone turnover action, and we suggest that PTHrP as a facilitator of oncogenes would be a novel target for therapeutic purposes.

New concepts in the formation, regulation of release, and metabolism of parathyroid hormone

New information has elucidated many of the biochemical pathways in the formation, release and metabolism of parathyroid hormone (PTH). The hormone is biosynthesized in the parathyroid cells from two distinct precursors, or prohormones, that are modified by specific enzymic cleavages during the synthesis and intracellular transport of the hormonal polypeptide. Release of the hormone from the gland inversely depends on the extracellular calcium concentration, but is regulated over a much narrower range of calcium concentration than was realized previously. This new information points to a pattern of regulation that is more appropriate for homeostasis than was the pattern indicated by earlier studies. The persistence of a basal level of PTH secretion, despite sustained hypercalcaemia, suggests a possible mechanism for the abnormal secretion seen in states of hyperparathyroidism. The discovery of a calium-dependent degradative pathway for PTH in the parathyroid cell indicates that changes in the turnover of PTH may be one means by which calcium regulates the amount of hormone available for secretion. Of the multiple immunoreactive forms of PTH present in the circulation of man and animals, the predominant form in blood appears to be a large biologically-inactive fragment consisting of the middle and carboxy two-thirds of the hormone sequence. At times, smaller biologically-active fragments of PTH may also appear in blood. Most circulating fragments of PTH probably arise from peripheral cleavage of the intact, secreted hormone in kidney and liver, but some forms of the hormone, including prohormones, may also be secreted from the parathyroid gland. The heterogeneity of circulating PTH and the concomitant uncertainties regarding its precise character have introduced difficulties in the interpretation of immunoassay measurements. A further delineation of the pathways and regulation of PTH biosynthesis, secretion and metabolism should lead to the development of more-specific immuno-assays and result in improved diagnosis and management of patients with disorders of the parathyroid glands.

Endocrine paraneoplastic syndromes in lung cancer

Lung tumors are capable of synthesizing and secreting peptide proteins (hormones) that lead to a variety of endocrine paraneoplastic syndromes. Knowledge about the clinical manifestations, pathophysiology, and treatment of these syndromes has evolved over time. This article provides an up-to-date overview of this knowledge.

Paraneoplastic syndromes associated with bronchogenic carcinoma

Paraneoplastic syndromes associated with lung cancer are diverse in their presentation, pathophysiology, and implications. They can be seen as a diagnostic and therapeutic challenge or as an opportunity to detect an otherwise asymptomatic malignancy. Unraveling the mechanisms that produce these syndromes will lead to insight into tumor biology that will be translated into novel approaches for early detection and therapy.

Parathyroid hormone-related protein

We review the current state of knowledge of the molecular properties and actions of parathyroid hormone-related protein (PTHrP) both in cancer patients and in normal physiology. PTHrP is a common product of squamous cancers and is the major mediator of the syndrome of humoral hypercalcemia of malignancy (HHM) by its actions through parathyroid hormone receptors in bone and kidney. Recently developed radioimmunoassays and tissue localization techniques indicate that PTHrP is produced by many more cancers than was originally indicated by clinical studies and that it contributes significantly to malignancy-related hypercalcemia associated with other etiologies, for example, cancers metastatic to bone and hematological malignancies. The gene encoding PTHrP is complex, with multiple exons coding for up to 12 alternate transcripts and three different length proteins, potentially in a tissue-specific manner, by the use of three promoters. Its expression is regulated by hormones and growth factors, and the untranslated exons display features in common with many cytokine genes. Although potential endocrine actions of PTHrP are evident in fetal development, further evidence suggesting that the normal physiological role of PTHrP is predominantly as a locally produced regulator/cytokine comes from localization studies and investigations of its actions in a variety of tissues. Such studies indicate that in addition to its parathyroid hormone-like actions, PTHrP has multiple activities, including those in fetal development, placental calcium transfer, lactation, smooth muscle relaxation, and on epithelial cell growth. Although PTHrP was discovered because of its production by cancers, evidence for its actions as a local regulator highlights the importance of understanding its roles not only in the etiology of HHM in cancer patients but also in normal tissues.

Renal cell carcinoma in tissue culture secretes nondialyzable product that stimulates bone resorption in organ-cultured mouse calvaria

The bone-resorbing capacity of human renal cell carcinomas in vitro has been examined. Bone resorption in cultures of mouse calvarial bones was assessed by the release of 45Ca from bones prelabeled in vivo and the mobilization of stable calcium and inorganic phosphate from nonlabeled bones. In addition, bone organic matrix degradation was determined either by the release of 3H from [3H]proline-labeled bones or by the loss of hydroxyproline from bone explants during culture. Tumor tissue-conditioned media (TCM) from 13 of 13 renal cell carcinomas stimulated bone resorption in a dose-dependent manner. From 5 of 13 kidneys with renal cell carcinoma, normal kidney cortex tissue was cultured and 4 of these 5 also produced bone-resorbing activity, but the amount was much less compared with the tumor tissue. The stimulatory effect of TCM on 45Ca release could be observed first after 12-24 h of culture. The effect could be inhibited by calcitonin but not by inhibitors of prostaglandin synthesis. The production of bone-resorbing activity by tumor cells could be inhibited by indomethacin and meclofenamic acid. In some tumors, the inhibition by indomethacin was total, whereas in other tumors only partial inhibition could be obtained. In 3 of 4, TCM bone-resorbing activity could be found in the retentate after dialysis. The results show that fresh human renal cell carcinoma tissue can elaborate prostanoid as well as nonprostanoid products that can stimulate bone resorption.

Parathyroid hormone-related protein: isolation, molecular cloning, and mechanism of action

Many factors, such as interleukin 1, TGF alpha, tumor necrosis factor alpha and beta, and PGs, have been implicated in etiological roles in HHM (Martin and Mundy, 1987). Much interest in the past has also centered upon the likelihood of ectopic secretion of PTH in this condition. We have purified a protein (PTHrP) implicated in HHM from a human lung cancer cell line (BEN). Full-length cDNA clones have been isolated and were found to encode a prepropeptide of 36 amino acids and a mature protein of 141 amino acids. Eight of the first 13 amino acids were identical with human PTH, although antisera directed to the NH2 terminus of PTHrP do not recognize PTH; this homology is not maintained in the remainder of the molecule. PTHrP therefore represents a previously unrecognized hormone, possibly related to the PTH gene by a gene duplication mechanism. In support of this notion, the PTHrP gene has been localized to the short arm of chromosome 12; it is believed that chromosome 11, containing the PTH gene, and chromosome 12 are evolutionarily related. In addition, the human PTHrP gene has been isolated, characterized, and shown to have a similar intron--exon organization as the PTH gene. It is possible that the original ancestral gene is indeed the PTHrP gene; resolution of this question awaits studies in lower species. Peptides synthesized to the predicted protein sequence have enabled detailed structure-function studies that have identified NH 2-terminal sequences to be responsible for the biological effects of the molecule. Antibodies raised against the various synthetic peptides have led to the immunohistochemical localization of PTHrP in many human squamous cell carcinomas as well as in a subpopulation of keratinocytes of normal skin. The availability of these antibodies has opened the way for the development of a radioimmunoassay to detect PTHrP in the sera of cancer patients at risk of developing hypercalcemia. The recent characterization of PTHrP-like activity in the ovine fetus suggests some physiological function for PTHrP. It is possible that PTHrP, as the fetal counterpart of PTH, has the role of maintaining the maternal-fetal calcium gradient. The isolation and characterization of PTHrP have added to our understanding of the mechanisms of hypercalcemia and may contribute to the understanding of other metabolic bone diseases, such as osteoporosis and Paget's disease. Finally, and perhaps most importantly, PTHrP may play a hitherto unrecognized role in normal cell physiology.

Parathyroid hormone-related protein: a novel gene product

Many factors, such as interleukin 1, transforming growth factor alpha, tumour necrosis factor alpha and beta, and prostaglandins, have been implicated in the pathogenesis of the humoral hypercalcaemia of malignancy (Mundy and Martin, 1982; Martin and Mundy, 1987; Mundy et al, 1984). Much interest in the past has also centred upon the likelihood of ectopic secretion of PTH in this condition. We have purified a protein (PTHrP) implicated in HHM from a human lung cancer cell line (BEN). Full-length cDNA clones have been isolated and found to encode a pre-pro-peptide of 36 amino acids and a mature protein of 141 amino acids. Eight of the first 13 amino acids were identical with human PTH, although antisera directed to the aminoterminus of PTHrP do not recognize PTH; this homology is not maintained in the remainder of the molecule. PTHrP therefore represents a previously unrecognized hormone, possibly related to the PTH gene by a gene duplication mechanism. In support of this notion, the PTHrP gene has been localized to the short arm of chromosome 12; it is believed that chromosome 11, containing the PTH gene, and chromosome 12 are evolutionarily related. In addition, the human PTHrP gene has been isolated, characterized, and shown to have an intron-exon arrangement that is more complex than the PTH gene. It is possible that the original ancestral gene is indeed the PTHrP gene; resolution of this question awaits studies in lower species. Peptides synthesized to the predicted protein sequence have allowed detailed structure-function studies that have identified aminoterminal sequences to be responsible for the biological effects of the molecule. Antibodies raised against the various synthetic peptides have led to the immunohistochemical localization of PTHrP in many human squamous cell carcinomas as well as in a subpopulation of keratinocytes of normal skin. The availability of these antibodies has opened the way for the development of a radioimmunoassay to detect PTHrP in the sera of cancer patients at risk of developing hypercalcaemia. The recent characterization of PTHrP-like activity in the ovine fetus suggests some physiological function for PTHrP. It is possible that PTHrP, as the fetal counterpart of PTH, has the role of maintaining the maternal-fetal calcium gradient. The isolation and characterization of PTHrP has added to our understanding of the mechanisms of hypercalcaemia and may contribute to the understanding of other metabolic bone diseases, such as osteoporosis and Paget's disease. Finally, and perhaps most importantly, PTHrP may play a hitherto unrecognized role in normal cell physiology.

A parathyroid hormone-related protein implicated in malignant hypercalcemia: cloning and expression

Humoral hypercalcemia of malignancy is a common complication of lung and certain other cancers. The hypercalcemia results from the actions of tumor factors on bone and kidney. We report here the isolation of full-length complementary DNA clones of a putative hypercalcemia factor, and the expression from the cloned DNA of the active protein in mammalian cells. The clones encode a prepro peptide of 36 amino acids and a mature protein of 141 amino acids that has significant homology with parathyroid hormone in the amino-terminal region. This previously unrecognized hormone may be important in normal as well as abnormal calcium metabolism.

Influence of serum Ca concentration on circulating molecular forms of PTH in three species

The influence of serum calcium concentration on total circulating parathyroid hormone (PTH) and on the relative amount of intact PTH-(1-84) and large carboxyterminal fragments was studied in the canine and bovine species and in man. Serum calcium was modified through infusions of CaCl2 or EDTA and samples obtained in time for the measurement of serum calcium and PTH concentrations. Pools of serum, corresponding to specific serum calcium concentrations, were analyzed by gel chromatography in all species. PTH was measured with a carboxyterminal radioimmunoassay. In basal conditions, total serum PTH was composed mostly of large carboxyterminal fragments, intact PTH-(1-84) representing less than 25% of the hormone in any species. With hypercalcemia, (greater than or equal to 2.0 mg/dl), total serum PTH decreased only to 40% of the original value measured in all species, despite serum calcium concentrations of over 13 mg/dl. The relative amount of intact PTH-(1-84) remained unchanged in the bovine and canine species and slightly decreased in man. Hypocalcemia (less than or equal to 2.0 mg/dl) induced a 300-450% increase in the basal PTH value measured. The relative amount of intact PTH-(1-84) became as or more important than carboxyterminal fragments in the canine species and in man, respectively, and remained slightly less in the bovine species. Despite small quantitative variations between species, these results indicate that changes in serum calcium concentration induced acute modification in PTH secretion or PTH peripheral metabolism, altering the ratio of intact hormone to carboxyterminal fragments in circulation.

Humoral hypercalcemia of malignancy. Release of a prostaglandin-stimulating bone-resorbing factor in vitro by human transitional-cell carcinoma cells

Secretion by tumor cells of circulating bone-resorbing factors may frequently underlie the hypercalcemia that occurs in patients with malignancy. Efforts to identify the responsible mediators have been hampered by a lack of available human tumor cell systems suitable for study of the pathogenesis of the humoral hypercalcemia syndrome. We have established a transitional-cell carcinoma (TCC) line in vitro from a patient with humoral hypercalcemia. These cells are tumorigenic and cause hypercalcemia in athymic nude mice. Culture medium conditioned by TCC cells contains potent bone-resorbing activity in vitro, the physical and biological properties of which are similar to those of bone-resorbing activity present in the original patient's urine. The bone-resorbing activity of the TCC factor is accompanied by increased prostaglandin release from bone and is blocked by indomethacin and calcitonin. The TCC-derived bone-resorbing activity coelutes with prostaglandin-stimulating activity during gel filtration with an approximate molecular weight of 15,000. This activity is nondialyzable, stable to concentrated urea and reducing agents, and destroyed by boiling. The TCC factor does not increase cyclic AMP production in bone or kidney bioassays and does not exhibit transforming growth factor activity. We conclude that a unique macromolecular factor released by TCC cells causes bone resorption by a mechanism dependent upon stimulation of bone cell cyclooxygenase, and that this factor is the probable cause of the hypercalcemia in vivo. The TCC cell line provides a new model for study of the human humoral hypercalcemia syndrome.

Tumor markers: value and limitations in the management of cancer patients

Sixteen tumor markers are reviewed, and measured to the ideal: produced by the tumor cell alone absent in health and in benign disease present in all patients with a given malignancy level in the blood representative of tumor mass detectable in occult disease. The only marker that approaches the ideal is human chorionic gonadotropin (HCG) in gestational trophoblastic tumors. In this malignancy, the HCG level suggests the diagnosis and stage, confirms response to therapy, and predicts relapse. The three most widely used and intensely studied tumor markers are carcinoembryonic antigen (CEA), alphafetoprotein (AFP), and HCG. CEA cannot be used in screening for cancer, but in carcinoma of the colon its elevation preoperatively increases the likelihood of advanced disease and postoperative recurrence. Postoperatively, elevated titers are often but not invariably associated with recurrent disease. AFP and HCG are useful in the management of nonseminomatous germ cell testicular tumors. Like CEA, they cannot be used for screening. They are more likely to be increased with advancing stage, and after therapy rising levels almost always mean recurrent disease. Some markers are valuable in specific circumstances, such as calcitonin in screening for familial medullary carcinoma of the thyroid. In multiple myeloma, immunoglobulins are useful in determining the tumor mass and response to therapy. In neuroblastoma, catecholamine metabolites are useful primarily in making the diagnosis. In some malignancies, the absence of effective therapy lowers the value of the marker, as for AFP in hepatoma. The remaining markers are too unreliable or too little studied to be useful in the management of an individual patient with cancer. The purpose of this paper is to provide the clinician with an understanding of the limitations of the present tumor markers that will lead to wiser use of the tests, and to provide standards to which future tumor markers should be measured.

Hypercalcaemia in the accelerated phase of chronic myelogenous leukaemia: no relationship to the phenotype of the blast cells

2 patients with chronic myelogenous leukaemia developed hypercalcaemia and severe myelofibrosis in the terminal phases of their disease. Hormonal studies excluded the hypercalcaemia being caused by primary hyperparathyroidism or ectopic parathyroid hormone secretion. Its development was unrelated to the phenotype of the blast cells, as assessed by conventional cytochemistry and immunological surface typing. The finding of increased urinary cAMP excretion in 1 of the patients suggests a circulating, nonparathyroid humoral bone resorbing factor with partial biological PTH-activity to be one of the pathogenetic mechanisms responsible for the occurrence of hypercalcaemia in patients with chronic myelogenous leukaemia.

Parathyroid hormone-like bioactivity in a patient with severe osteitis fibrosa cystica due to malignancy: renotropic actions of a tumour extract as assessed by cytochemical bioassay

A patient is described with malignancy, hypercalcaemia and radiological evidence of severe parathyroid bone disease but undetectable concentrations of circulating immunoreactive PTH. Autopsy showed the tumour to be a metastatic bronchial carcinoid with no evidence of primary parathyroid disease. Extracts of the tumour had no PTH immunoreactivity but had high concentrations of a substance with identical activity to PTH in a cytochemical bioassay. The biological activity of the extract was not inhibited by PTH antibodies but was inhibited by an antagonist to PTH bioactivity.

Malignant lymphoma, small non-cleaved, non-Burkitt's type

An autopsy case of "Malignant lymphoma, small non-cleaved, non-Burkitt's type" with hypercalcemia is presented. A 57-year-old Japanese man suffering from epigastralgia and "retroperitoneal tumor" for nine months was found at autopsy to have two large tumor masses in the retroperitoneum and pelvic cavity. Tumor cell infiltration into the liver, spleen, both kidneys, and both adrenal glands was observed on microscopic examination. The tumor cells were lymphoid cells with the characteristics of "Malignant lymphoma, small non-cleaved, non-Burkitt's type". The importance of recognizing non-Burkitt's type is pointed out. The cause of the presence of hypercalcemia is also discussed.

Differential laboratory diagnosis of hypercalcemia

It is proposed that this review will adopt the following format: establishment of hypercalcemia. This demands a discussion of the problem of normal ranges, the usage of either total calcium or ionized calcium in making this decision and where total calcium is used whether adjustment of this value for serum protein concentration should be used and if so, the formulae which have been cited to perform this. Having established hypercalcemia why is it necessary to differentiate this? This will involve reviewing those clinical situations in which differentiation of hypercalcemia has been attempted and will include an attempt to produce an up to date indication of conditions in which hypercalcemia has been described. When hypercalcemia has been established the laboratory tests which have been further used to discriminate will be divided into single tests such as N- or C- terminal parathormone, 1,25- dihydroxycholecalciferol, cyclic AMP; the combination tests which have been used including phosphate clearance, chloride vs. bicarbonate etc. proceeding to those groups which have used discriminant function to help in the decision making; dynamic testing will also be discussed particularly with reference to steroid suppression but will also include other known suppressants such as Mithramycin and Calcitonin. A final section will be included attempting to assess overall the present state of art in differentiating laboratory diagnosis of hypercalcemia and will also attempt to highlight those areas which appear to be most fruitful areas of progress in the future.

The reasons for persistent hypercalcaemia after cervical exploration for presumed primary hyperparathyroidism

Of 500 consecutive patients who underwent cervical exploration for presumed primary hyperparathyroidism, 461 (92.2 per cent) were cured, as judged by an immediate return of serum calcium levels to normal. Thirty-nine patients (7.8 per cent) had persistent hypercalcaemia after the initial operation. The clinical profiles, operative and pathologic findings, surgical procedures performed and subsequent management of these 39 patients were reviewed. At reevaluation, 4 patients were noted to have been cured of their hyperparathyroidism. Twenty-one patients had persistent hyperparathyroidism: in 6, all 4 parathyroid glands had not been identified at the initial operation and in 15, hypercalcaemia persisted after the identification of 4 glands. One patient had recurrent hyperparathyroidism after the removal of a 720 mg adenoma and the identification of 3 normal parathyroid glands. Nine patients had nonparathyroid causes for the hypercalcaemia: 2 had occult malignant neoplasms, 6 had benign familial hypocalciuric hypercalcaemia and 1 had immobilization hypercalcaemia. In 4 patients the reason for the persistent hypercalcaemia remained unclear. We suggest a schema that may be used as a guideline in the investigation and management of patients with persistent hypercalcaemia after primary neck exploration for presumed hyperparathyroidism.

Identification of adenylate cyclase-stimulating activity and cytochemical glucose-6-phosphate dehydrogenase-stimulating activity in extracts of tumors from patients with humoral hypercalcemia of malignancy

Humoral hypercalcemia of malignancy (HHM) most commonly results from secretion by tumors of an unidentified circulating calcemic factor that appears in clinical studies to stimulate both a parathyroid hormone (PTH)-sensitive proximal tubular adenylate cyclase and a distinct PTH-sensitive renal tubular glucose-6-phosphate dehydrogenase complex. In the present study, 8 M urea extracts of tumors from patients with HHM have been shown to contain both in vitro adenylate cyclase-stimulating activity and glucose-6-phosphate dehydrogenase-stimulating activity as detected in a sensitive cytochemical bioassay. Both the adenylate cyclase-stimulating activity and cytochemical bioactivity are due to specific binding of a substance in the tumor extracts to renal PTH receptors, as demonstrated by competitive inhibition studies using the bovine PTH fragment analogue [Nle8,18, Tyr34]bPTH-(3-34) amide. Preincubation with an antiserum to PTH results in no loss of activity in the tumor extract, and the activity appears both on gel filtration and ultrafiltration to be far larger than PTH (estimated Mr 70,000). These studies demonstrate that extracts of tumors from patients with HHM contain a substance that binds to the PTH receptors in the nephron responsible for activation of both the PTH-sensitive glucose-6-phosphate dehydrogenase and the PTH-sensitive adenylate cyclase. This substance is chromatographically and immunologically distinct from PTH. Its role in the genesis of HHM requires further study.

Human renal carcinoma cells produce hypercalcemia in the nude mouse and a novel protein recognized by parathyroid hormone receptors

When grown in nude mice, cultured renal carcinoma cells from a hypercalcemic patient produced marked hypercalcemia that was reversed by resection of tumor. Conditioned medium from this cell line contained a protein with activity in a renal adenylate cyclase bioassay for parathyroid hormone (PTH) which was blocked by the competitive PTH antagonist [8norleucyl, 18norleucyl, 34tyrosinyl]bPTH (3-34)amide. However, the biologically active protein was eluted from gel filtration columns as a larger molecular size component that PTH and was not recognized by any of four region-specific PTH antisera. The properties of this factor resemble those of the postulated PTH-like substance(s) in humoral hypercalcemia of malignancy.

The hypercalcemia of malignancy: pathogenesis and management

The number of agents and treatment regimens which can be used in the medical treatment of hypercalcemia has increased markedly over the last 5 yr. As this list has increased, clinicians are anxious to know more about the humoral and cellular mechanisms which are responsible for the hypercalcemia of malignancy and to understand how these drugs work. Unfortunately there is no treatment available presently which is uniformally safe and effective, and the potential pathogenetic mechanisms responsible for hypercalcemia are hotly debated. In this review, we plan to summarize current views of the pathogenesis, clinical features and treatment of hypercalcemia associated with malignant disease.

Disorders of calcium and magnesium homeostasis

The components of calcium and magnesium balance and the factors responsible for the maintenance of the serum concentration of these cations are reviewed. Within this framework, the causes and treatment of disturbances of the serum concentration are discussed. Hypercalcemia is usually a reflection of increased bone resorption and/or gut absorption with the kidney playing a secondary role. Hypocalcemia is usually due to either a disturbance in the parathyroid hormone-adenylate cyclase system or a disturbance in vitamin D metabolism. As vitamin D is required for expression of the action of PTH at bone and as PTH is a prime regulator of vitamin D metabolism, the absence of either component results in important disturbances in calcium balance. In contrast to calcium homeostasis, the kidney plays a major role in the determination and regulation of serum magnesium. The major causes of hypermagnesemia therefore are associated with loss of renal function, and hypomagnesemia is frequently due to renal magnesium wasting.

Primary squamous cell carcinoma of the thyroid associated with marked leukocytosis and hypercalcemia

In a 71-year-old woman with primary squamous cell carcinoma of the thyroid, marked leukocytosis (26,000 to 87,000/mm3), in which about 90% were mature neutrophils, was observed. Hypercalcemia (about 12 mg/100 ml) was also observed with the serum inorganic phosphate within normal limits. The serum parathyroid hormone (PTH) was undetectable. The thyroid tumor was successfully transplanted to athymic nude mice at autopsy. Marked leukocytosis and hypercalcemia was reproduced in the tumor-bearing nude mice. The result indicates that the thyroid cancer was secreting humoral factors(s) producing leukocytosis and hypercalcemia. The association of leukocytosis and hypercalcemia has been reported in the two similar cases of squamous cell carcinoma, in which the tumor was proven to secrete colony-stimulating factor (CSF). Leukocytosis and hypercalcemia may thus form a new paraneoplastic syndrome.

Hypercalcemia complicating small-cell carcinoma

Hypercalcemia is a common paraneoplastic syndrome complicating some varieties of lung cancer. It has rarely been reported with small-cell carcinoma of the lung. Seven cases of hypercalcemia complicating small-cell carcinoma of the lung are described; clinical features indicate that significant bone or bone marrow involvement is present in all cases. Parathormone assays were found to be generally in the normal range, though inappropriate for the levels of hypercalcemia.

Locating a parathyroid adenoma by ultrasonography and aspiration biopsy cytology

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Biochemical evaluation of patients with cancer-associated hypercalcemia: evidence for humoral and nonhumoral groups

In 50 consecutive patients with cancer-associated hypercalcemia, we measured nephrogenous cyclic AMP, tubular phosphorus threshold, fasting calcium excretion, plasma 1,25-dihydroxyvitamin D, and immunoreactive parathyroid hormone as determined by four region-specific antiserums. Nephrogenous cyclic AMP excretion was elevated in 41 patients and suppressed in nine (means, 5.85 vs. 0.51 nmol per 100 ml of glomerular filtrate). There was no overlap between these groups. When compared with 15 patients with primary hyperparathyroidism, the group with increased cyclic AMP excretion had similar reductions in tubular phosphorus threshold; higher fasting calcium excretion (means, 0.66 vs. 0.25 mg per 100 ml of glomerular filtrate, P < 0.01); marked reductions in 1,25-dihydroxyvitamin D (means, 20 vs. 83 pg per milliliter, P < 0.001); and lower levels of immunoreactive parathyroid hormone in all four assays. The data suggest that elevated excretion of nephrogenous cyclic AMP may be a useful marker of humorally mediated cancer-associated hypercalcemia, that this type of hypercalcemia is common, that the humoral factor responsible for this syndrome is not native 1-84 parathyroid hormone, and that the various subtypes of cancer-associated hypercalcemia are biochemically distinguishable from primary hyperparathyroidism.

Hypercalcaemia in malignancy

The pathogenesis of cancer hypercalcaemia is an enigma that continues to challenge clinical investigators. Several possible mediators and pathways seem to be operating. To date, humoral and cellular mediators have been found to arise in tumour or normal tissues. The pathophysiological pathways that lead to osteolysis and hypercalcaemia are in large part determined by the biology of the specific tumour. Thus, the mechanisms that give rise to osteolysis in a metastatic breast cancer may be distinct from those that are operating in a non-metastatic lung carcinoma. The morbid consequences of excessive osteolysis and hypercalcaemia are usually similar and require prompt attention. Current research holds out the promise of identifying the agents and pathways responsible for cancer hypercalcaemia. Therapies may one day exist which arrest the specific pathophysiological processes which are operating.

Development of sequence specific radioimmunoassay of human parathyroid hormone and its use in the diagnosis of hyperparathyroidism

Two antisera which were raised against bovine parathyroid hormone (bPTH), and which cross-reacted with the human hormone, have been characterized. The antisera which originated from rooster and guinea-pig, were found to contain several populations of antibodies directed against both N-terminal and C-terminal sequences of the hormone. However, at proper dilutions the rooster antiserum did not bind the N-terminal fragment nor could this fragment displace the [125I] bPTH (1--84 amino acid residue) from binding to the antiserum. Furthermore, preincubation experiments with excess N-terminal fragment showed only a negligible reduction in maximal binding of the iodinated intact hormone using the rooster antiserum. In contrast, the guinea-pig antiserum reacted equally well with the N-terminal fragment and the intact hormone, and preincubation with this fragment reduced the binding of the [125I]bPTH (1--84 amino acid residues) by 75%. Gel filtration of hyperparathyroid serum on Bio-Gel P-60 showed immunoreactive material which was measured with both antisera, eluting at a position similar to the intact hormone. However, in the C-terminal specific, but not in the N-terminal specific radioimmunoassay the major component eluted together with or somewhat earlier than the N-terminal bPTH fragment (1--34 amino acid residue), and this peak represented more than 90% of total immunoreactive PTH (iPTH) in serum. This major iPTH component must therefore represent fragment(s) with intact carboxy-terminal sequences. The N-terminal specific radioimmunoassay was unable to measure iPTH in about 80--90% of healthy individuals while the C-terminal specific assay detected iPTH in about 88% of these sera (equal to or above 0.1 micrograms/l). Similarly, the N-terminal specific antiserum measured consistently lower serum iPTH concentrations in patients with primary hyperparathyroidism. In thirty-four out of forty-one patients with surgically verified primary hyperparathyroidism, serum iPTH concentrations equal to or above 0.60 micrograms/l were demonstrated using the C-terminal, specific radioimmunoassay.