Pharmacological Npt2a Inhibition Causes Phosphaturia and Reduces Plasma Phosphate in Mice with Normal and Reduced Kidney Function.

BACKGROUND: The kidneys play an important role in phosphate homeostasis. Patients with CKD develop hyperphosphatemia in the later stages of the disease. Currently, treatment options are limited to dietary phosphate restriction and oral phosphate binders. The sodium-phosphate cotransporter Npt2a, which mediates a large proportion of phosphate reabsorption in the kidney, might be a good therapeutic target for new medications for hyperphosphatemia. METHODS: The authors assessed the effects of the first orally bioavailable Npt2a inhibitor (Npt2a-I) PF-06869206 in normal mice and mice that had undergone subtotal nephrectomy (5/6 Nx), a mouse model of CKD. Dose-response relationships of sodium, chloride, potassium, phosphate, and calcium excretion were assessed in response to the Npt2a inhibitor in both groups of mice. Expression and localization of Npt2a/c and levels of plasma phosphate, calcium, parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF-23) were studied up to 24-hours after Npt2a-I treatment. RESULTS: In normal mice, Npt2a inhibition caused a dose-dependent increase in urinary phosphate (ED50 approximately 21 mg/kg), calcium, sodium and chloride excretion. In contrast, urinary potassium excretion, flow rate and urinary pH were not affected dose dependently. Plasma phosphate and PTH significantly decreased after 3 hours, with both returning to near baseline levels after 24 hours. Similar effects were observed in the mouse model of CKD but were reduced in magnitude. CONCLUSIONS: Npt2a inhibition causes a dose-dependent increase in phosphate, sodium and chloride excretion associated with reductions in plasma phosphate and PTH levels in normal mice and in a CKD mouse model.

Acute Adaption to Oral or Intravenous Phosphate Requires Parathyroid Hormone.

Phosphate (Pi) homeostasis is regulated by renal, intestinal, and endocrine mechanisms through which Pi intake stimulates parathyroid hormone (PTH) and fibroblast growth factor-23 secretion, increasing phosphaturia. Mechanisms underlying the early adaptive phase and the role of the intestine, however, remain ill defined. We investigated mineral, endocrine, and renal responses during the first 4 hours after intravenous and intragastric Pi loading in rats. Intravenous Pi loading (0.5 mmol) caused a transient rise in plasma Pi levels and creatinine clearance and an increase in phosphaturia within 10 minutes. Plasma calcium levels fell and PTH levels increased within 10 minutes and remained low or high, respectively. Fibroblast growth factor-23, 1,25-(OH)2-vitamin D3, and insulin concentrations did not respond, but plasma dopamine levels increased by 4 hours. In comparison, gastric Pi loading elicited similar but delayed phosphaturia and endocrine responses but did not affect plasma mineral levels. Either intravenous or gastric loading led to decreased expression and activity of renal Pi transporters after 4 hours. In parathyroidectomized rats, however, only intravenous Pi loading caused phosphaturia, which was blunted and transient compared with that in intact rats. Intravenous but not gastric Pi loading in parathyroidectomized rats also led to higher creatinine clearance and lower plasma calcium levels but did not reduce the expression or activity of Pi transporters. This evidence suggests that an intravenous or intestinal Pi bolus causes rapid phosphaturia through mechanisms requiring PTH and downregulation of renal Pi transporters but does not support a role of the intestine in stimulating renal clearance of Pi.

Hyperparathyroidism and increased fractional excretion of phosphate predict allograft loss in long-term kidney transplant recipients.

BACKGROUND: After kidney transplantation, fibroblast growth factor-23 (FGF-23) normally returns to baseline within 1 year whereas hyperparathyroidism persists in most kidney transplant (KT) recipients. As a result, serum phosphate remains relatively low in association with increased serum calcium and urinary phosphate excretion when compared to chronic kidney disease patients. The relationship between mineral metabolism and outcomes in long-term KT recipients has not been extensively studied. This study investigated whether the alteration in mineral metabolism influenced graft survival in long-term KT recipients. METHODS: This study included 273 KT recipients after 1 year of transplantation. Mineral parameters were obtained at the time of enrolment and patients were followed prospectively for an average of 71 months. RESULTS: Graft loss (death-censored) occurred in 41 (15%) patients. In univariate analysis, deceased donor transplantation, decreased serum albumin and estimated glomerular filtration rate, increased serum phosphate, parathyroid hormone (PTH), FGF-23 and fractional excretion of phosphate (FePi) predicted future allograft loss. After adjustments for cardiovascular disease risk factors, donor type, dialysis vintage, serum albumin and allograft function, only increased PTH and FePi remained associated with the outcome. Relationships between increased serum phosphate and FGF-23 with graft survival were lost after adjustments. Adjusted survival curves revealed the association between PTH > 90 pg/mL and FePi > 20% with worse graft survival. CONCLUSIONS: Hyperparathyroidism and increased FePi predicted allograft loss in long-term KT recipients.

Identification of a novel FN1-FGFR1 genetic fusion as a frequent event in phosphaturic mesenchymal tumour.

Phosphaturic mesenchymal tumours (PMTs) are uncommon soft tissue and bone tumours that typically cause hypophosphataemia and tumour-induced osteomalacia (TIO) through secretion of phosphatonins including fibroblast growth factor 23 (FGF23). PMT has recently been accepted by the World Health Organization as a formal tumour entity. The genetic basis and oncogenic pathways underlying its tumourigenesis remain obscure. In this study, we identified a novel FN1-FGFR1 fusion gene in three out of four PMTs by next-generation RNA sequencing. The fusion transcripts and proteins were subsequently confirmed with RT-PCR and western blotting. Fluorescence in situ hybridization analysis showed six cases with FN1-FGFR1 fusion out of an additional 11 PMTs. Overall, nine out of 15 PMTs (60%) harboured this fusion. The FN1 gene possibly provides its constitutively active promoter and the encoded protein's oligomerization domains to overexpress and facilitate the activation of the FGFR1 kinase domain. Interestingly, unlike the prototypical leukaemia-inducing FGFR1 fusion genes, which are ligand-independent, the FN1-FGFR1 chimeric protein was predicted to preserve its ligand-binding domains, suggesting an advantage of the presence of its ligands (such as FGF23 secreted at high levels by the tumour) in the activation of the chimeric receptor tyrosine kinase, thus effecting an autocrine or a paracrine mechanism of tumourigenesis.

Acquired disorders of phosphaturia: Beyond tumor-induced osteomalacia.

Phosphate is an integral part of human cellular structure and function. Though most recognised disorders of phosphaturia are genetic in origin, phosphate loss due to acquired conditions is commonly encountered in clinical practice. Acquired hypophosphatemia is most commonly due to renal phosphate wasting and can produce significant morbidity. It also heralds future kidney damage, and continued exposure can lead to progressive kidney injury and potentially renal failure. These conditions are a diverse group of disorders with common shared mechanisms causing loss of phosphate in the urine. Renal phosphate loss can occur as an isolated entity or as a part of generalised proximal tubular dysfunction, i.e., Fanconi's syndrome. An insight into the pathophysiological mechanisms of acquired phosphaturia can help clinicians monitor their patients better and avoid potential harms.

[Ostemalacia due to a tumor secreting FGF-23]. / Osteomalacia por tumor secretor de FGF-23.

A case of oncogenic osteomalacia in a 50-year-old male is here presented. He suffered severe bone pain and marked muscular weakness of 4 years' duration. There were several vertebral deformities in the thoracic spine, bilateral fractures of the iliopubic branches, another fracture in the left ischiopubic branch, and a Looser's zone in the right proximal tibia. An octreotide-Tc scan allowed to identify a small tumor in the posterior aspect of the right knee. It was surgically removed. Microscopically, it was a phosphaturic mesenchymal tumor-mixed connective tissue (PMT-MCT). Expression of FGF-23 was documented by immune-peroxidase staining. There was rapid improvement, with consolidation of the pelvic fractures and the tibial pseudo-fracture. The laboratory values returned to normal.

Renal function in patients with ß-thalassaemia major: a long-term follow-up study.

BACKGROUND: Little information is available about the kidney's involvement in patients with ß-thalassaemia major (TM). In particular, there are no studies reporting the outcome of renal function over time. METHODS: In this retrospective study, we evaluated the changes in estimated glomerular filtration rate (eGFR) in 81 adult patients with TM followed for 10 years. Only patients who had an eGFR of >90 mL/min/1.73 m(2) at presentation were admitted to the study. All patients were regularly followed for at least 10 years. RESULTS: At 10 years, 66 patients showed a mild decline in eGFR that remained, however, within a normal range (from 119.9 to 113.6 mL/min/1.73 m(2), P = 0.636). In the remaining 15 patients (18.5%), eGFR decreased to <90 mL/min (from 98.1 to 78.2 mL/min/1.73 m(2); P = 0.004). The repeated-measures models showed that the decline in eGFR over time was significantly higher (P = 0.0068) in patients with baseline phosphaturia >1000 mg/24 h (P = 0.0068), while eGFR tended to decline more rapidly in patients with baseline uricuria >700 mg/24 h than in those with lower uricuria (P = 0.0783). Univariate Cox's proportional regression models showed that abnormal levels of calcaemia were associated with the risk of kidney damage [hazard ratio (HR) 0.30, 95% confidence interval 0.09-0.97 for calcaemia 8.4-10.2 mg/dL versus HR not estimable for calcaemia <8.4 or >10.2 mg/dL]. CONCLUSIONS: In most adults with TM, the eGFR tends to remain within a normal range after 10 years. However, patients with elevated phosphaturia, elevated uricuria and/or abnormal levels of calcaemia show a significant decline in eGFR over time, suggesting that tubular damage acquired in childhood caused by either TM or its treatment may eventually result in abnormal eGFR. Further studies in a larger cohort of TM patients are needed to further elucidate the long-term impact of TM on renal function.

PKB/SGK-resistant GSK3 enhances phosphaturia and calciuria.

Insulin and IGF1-dependent signaling activates protein kinase B and serum and glucocorticoid inducible kinase (PKB/SGK), which together phosphorylate and inactivate glycogen synthase kinase GSK3. Because insulin and IGF1 increase renal tubular calcium and phosphorus reabsorption, we examined GSK3 regulation of phosphate transporter activity and determined whether PKB/SGK inactivates GSK3 to enhance renal phosphate and calcium transport. Overexpression of GSK3 and the phosphate transporter NaPi-IIa in Xenopus oocytes decreased electrogenic phosphate transport compared with NaPi-IIa-expressing oocytes. PKB/SGK serine phosphorylation sites in GSK3 were mutated to alanine to create gsk3(KI) mice resistant to PKB/SGK inactivation. Compared with wildtype animals, gsk3(KI) animals exhibited greater urinary phosphate and calcium clearances with higher excretion rates and lower plasma concentrations. Isolated brush border membranes from gsk3(KI) mice showed less sodium-dependent phosphate transport and Na-phosphate co-transporter expression. Parathyroid hormone, 1,25-OH vitamin D levels, and bone mineral density were decreased in gsk3(KI) mice, suggesting a global dysregulation of bone mineral metabolism. Taken together, PKB/SGK phosphorylation of GSK3 increases phosphate transporter activity and reduces renal calcium and phosphate loss.

SGK3: a novel regulator of renal phosphate transport?

Phosphate is a key constituent of several important molecules, and hyperphospatemia has been associated with increased cardiovascular mortality. The kidney plays a crucial role in phosphate metabolism, as it is able to modulate phosphate excretion. Serum- and glucocorticoid-inducible kinase 3 (SGK3) has been shown to regulate a wide variety of transport systems. Bhandaru et al. suggest that SGK3 may have a significant role in the regulation of renal tubular phosphate transport.

Decreased bone density and increased phosphaturia in gene-targeted mice lacking functional serum- and glucocorticoid-inducible kinase 3.

Insulin and growth factors activate the phosphatidylinositide-3-kinase pathway, leading to stimulation of several kinases including serum- and glucocorticoid-inducible kinase isoform SGK3, a transport regulating kinase. Here, we explored the contribution of SGK3 to the regulation of renal tubular phosphate transport. Coexpression of SGK3 and sodium-phosphate cotransporter IIa significantly enhanced the phosphate-induced current in Xenopus oocytes. In sgk3 knockout and wild-type mice on a standard diet, fluid intake, glomerular filtration and urine flow rates, and urinary calcium ion excretion were similar. However, fractional urinary phosphate excretion was slightly but significantly larger in the knockout than in wild-type mice. Plasma calcium ion, phosphate concentration, and plasma parathyroid hormone levels were not significantly different between the two genotypes, but plasma calcitriol and fibroblast growth factor 23 concentrations were significantly lower in the knockout than in wild-type mice. Moreover, bone density was significantly lower in the knockouts than in wild-type mice. Histological analysis of the femur did not show any differences in cortical bone but there was slightly less prominent trabecular bone in sgk3 knockout mice. Thus, SGK3 has a subtle but significant role in the regulation of renal tubular phosphate transport and bone density.

Hypophosphatemia in acute liver failure of a broad range of etiologies is associated with phosphaturia without kidney damage or phosphatonin elevation.

Hypophosphatemia is a common and dangerous complication of acute liver failure (ALF) of various etiologies. While various mechanisms for ALF-associated hypophosphatemia have been proposed including high phosphate uptake into regenerating hepatocytes, acetaminophen (APAP)-associated hypophosphatemia was linked to renal phosphate wasting, and APAP-induced renal tubular injury was proposed as underlying mechanism. We studied 30 normophosphatemic and 46 hypophosphatemic (serum phosphate < 2.5 mg/dL) patients from the Acute Liver Failure Study Group registry with APAP- or non-APAP-induced ALF. Since kidney injury affects phosphate excretion, patients with elevated serum creatinine (>1.2 mg/dL) were excluded. Maximal amount of renal tubular phosphate reabsorption per filtered volume (TmP/GFR) was calculated from simultaneous serum and urine phosphate and creatinine levels to assess renal phosphate handling. Instead of enhanced renal phosphate reabsorption as would be expected during hypophosphatemia of non-renal causes, serum phosphate was positively correlated with TmP/GFR in both APAP- and non-APAP-induced ALF patients (R2 = 0.66 and 0.46, respectively; both P < 0.0001), indicating renal phosphate wasting. Surprisingly, there was no evidence of kidney damage based on urinary markers including neutrophil gelatinase-associated lipocalin and cystatin C even in the APAP group. Additionally, there was no evidence that the known serum phosphatonins parathyroid hormone, fibroblast growth factor 23, and α-Klotho contribute to the observed hypophosphatemia. We conclude that the observed hypophosphatemia with renal phosphate wasting in both APAP- and non-APAP-mediated ALF is likely the result of renal tubular phosphate leak from yet-to-be identified factor(s) with no evidence for proximal tubular damage or contribution of known phosphatonins.

Phosphaturic action of fibroblast growth factor 23 in Npt2 null mice.

In the present study, we evaluated the roles of type II and type III sodium-dependent P(i) cotransporters in fibroblast growth factor 23 (FGF23) activity by administering a vector encoding FGF23 with the R179Q mutation (FGF23M) to wild-type (WT) mice, Npt2a knockout (KO) mice, Npt2c KO mice, and Npt2a(-/-)Npt2c(-/-) mice (DKO mice). In Npt2a KO mice, FGF23M induced severe hypophosphatemia and markedly decreased the levels of Npt2c, type III Na-dependent P(i) transporter (PiT2) protein, and renal Na/P(i) transport activity. In contrast, in Npt2c KO mice, FGF23M decreased plasma phosphate levels comparable to those in FGF23M-injected WT mice. In DKO mice with severe hypophosphatemia, FGF23M administration did not induce an additional increase in urinary phosphate excretion. FGF23 administration significantly decreased intestinal Npt2b protein levels in WT mice but had no effect in Npt2a, Npt2c, and DKO mice, despite marked suppression of plasma 1,25(OH)(2)D(3) levels in all the mutant mice. The main findings were as follow: 1) FGF23-dependent phosphaturic activity in Npt2a KO mice is dependent on renal Npt2c and PiT-2 protein; 2) in DKO mice, renal P(i) reabsorption is not further decreased by FGF23M, but renal vitamin D synthesis is suppressed; and 3) downregulation of intestinal Npt2b may be mediated by a factor(s) other than 1,25(OH)(2)D(3). These findings suggest that Npt2a, Npt2c, and PiT-2 are necessary for the phosphaturic activity of FGF23. Thus complementary regulation of Npt2 family proteins may be involved in systemic P(i) homeostasis.

Physiological roles of CLC Cl(-)/H (+) exchangers in renal proximal tubules.

The CLC gene family encodes Cl(-) channels or Cl(-)/H(+) exchangers. While our understanding of their structure-function relationship has greatly benefited from the crystal structure of bacterial homologues, human inherited diseases and knock-out mice were crucial in deciphering their physiological roles. Several vesicular CLC Cl(-)/H(+) exchangers are expressed in the proximal tubule (PT). ClC-5 mutations cause Dent's disease which is associated with low molecular weight proteinuria and kidney stones. ClC-5 knock-out mice revealed impaired endocytosis as the primary defect in Dent's disease. It extends to receptor-mediated and fluid-phase endocytosis and entails changes in calciotropic hormones that result in kidney stones. No renal functions could be assigned so far to ClC-3 and ClC-4, which are also expressed in PTs. Loss of ClC-7 or its beta-subunit Ostm1 entails lysosomal storage in the PT, in addition to the neuronal lysosomal storage and osteopetrosis that are the hallmarks of ClC-7/Ostm1 loss in mice and men.

Oncogenic osteomalacia caused by a phosphaturic mesenchymal tumor of the thoracic spine.

Phosphaturic mesenchymal tumors that cause the paraneoplastic syndrome known as oncogenic osteomalacia are rare. The authors report on the case of a 57-year-old man with a history of osteomalacia and in whom was diagnosed a thoracic spine tumor at the T-4 level. Complete tumor resection was accomplished. The histological diagnosis was phosphaturic mesenchymal tumor (mixed connective tissue variant). After lesion removal, the paraneoplastic syndrome resolved. At the 24-month follow-up, no recurrence of the disease was observed. The clinical presentation, surgical technique, and follow-up in this case were reviewed in detail.

Matrix extracellular phosphoglycoprotein causes phosphaturia in rats by inhibiting tubular phosphate reabsorption.

BACKGROUND: Matrix extracellular phosphoglycoprotein (MEPE), first isolated from tumour-derived tissue from a patient with oncogenic hypophosphataemia, is a putative phosphatonin that has received much less attention than fibroblast growth factor-23. To date, its effect on renal tubular phosphate reabsorption remains undefined. METHODS: A renal clearance study was performed in anaesthetized rats infused intravenously with a range of doses of MEPE. RESULTS: MEPE had no effect on glomerular filtration rate (inulin clearance) but caused rapid, dose-dependent increases in absolute and fractional phosphate excretion, wholly attributable to reduced phosphate reabsorption. At a maximal dose, MEPE increased fractional phosphate excretion more than 2-fold, whereas no change was observed in time controls. CONCLUSION: The results lend support to the hypothesis that MEPE contributes to the phosphaturia of oncogenic hypophosphataemia and of hypophosphataemic rickets.

Growth hormone improves growth rate and preserves renal function in Dent disease.

Dent disease, an X-linked recessive renal tubular disease, results from loss-of-function mutations in the CLCN5 chloride channel gene. The effects of Dent disease on growth have not been described. We report siblings who presented with proteinuria, calciuria, and phosphaturia and growth failure who responded to growth hormone (GH) treatment. Genotyping revealed a novel c.2179delG frameshift mutation at codon 727, exon 12 of the CLCNS gene. Two years after initial presentation, linear growth had slowed, and evaluation revealed isolated GH deficiency. GH therapy resulted in more than two-fold increases in height velocity and serum IGF-I levels. There was no net change in estimated glomerular filtration rate, proteinuria or calciuria in response to GH therapy, but there was a delayed improvement in phosphaturia. These cases provide insight into the effects of GH on growth and renal function in Dent disease. Furthermore, we have reported a novel CLCN5 mutation.

Phosphaturic mesenchymal tumor and related wound problem.

INTRODUCTION: Phosphaturic mesenchymal tumor mixed connective tissue type (PMT/MCT) is the most common type (up to 90%) of phosphaturic mesenchymal tumor (PMT), a rare clinicopathologic entity. Besides overproduction of fibroblast growth factor 23 (FGF23), there is a big variation of immunohistochemical characteristic across types of PMT, which makes it difficult to obtain an early diagnosis of PMT/MCT. As a benign tumor, PMT/MCT usually happens in subcutaneous tissues and leads to nonhealing of wound. A complete excision of PMT/MCT facilitates wound healing. CONCLUSIONS: Review of the existing evidence indicates that early diagnosis of PMT/MCT is critically important when treating PMT/MCT wound. Hence standardization of early diagnosis for PMT/MCT is mandated.

Phosphaturic mesenchymal tumor of the nasal cavity and paranasal sinuses: A clinical curiosity presenting a diagnostic challenge.

Phosphaturic mesenchymal tumor (PMT) is a rare mesenchymal neoplasm associated with tumor-induced osteomalacia (TIO) and elevated serum FGF-23. Common in extremities, PMT rarely occurs in sinonasal region. We report a series of sinonasal PMT diagnosed at our institute over a 6-year period. Six cases of sinonasal PMT were identified during this period, of which five presented with features of TIO. Median age of patients was 45.5 years. All six tumors were composed of stellate to spindled cells, with prominent staghorn vasculature in four cases. Typical smudgy matrix was seen in all cases, but only focally; grungy calcification was absent. Accurate diagnosis of PMTs is imperative, as complete excision leads to dramatic resolution of TIO symptoms. Lack of knowledge of this entity prevents clinicians from ordering relevant investigations. Absence of specific morphological features, like grungy calcification, and presentation at atypical locations makes the diagnosis challenging. Awareness of this entity is essential in order to suspect PMT in patients presenting with a soft tissue mass and features of TIO, however unusual the location may be.

[The Power of Phosphaturia in the Infrequent Hemodialysis]. / L'importanza della Fosfaturia nei pazienti in Emodialisi Infrequente.

INTRODUCTION: Residual renal function (RRF) and phosphaturia had not stimulated particular interest in studies regarding patients on hemodialysis. In the current year the Authors have selected a series of patients with RRF undergoing infrequent hemodialysis treatments. PURPOSE: The Authors have carried out a study of the phosphate balance in patients on infrequent hemodialysis with the hypothesis that the phosphaturia was always neglected in hemodialysis patients, but it could represent a positive impact element on the cardiovascular events and mortality in hemodialysis. METHODS: During 6 months, the Authors have conducted forty urine collections in 10 patients on twice a week hemodialysis (TWH) (age: 69,3 years, dialysis vintage: 42,7 months and 40.9 months on TWH) and eighty urine collections in 8 patients on once a week hemodialysis and low-protein diet (CDDP) (age: 69.6 years, dialysis vintage: 24.7 months and 24 months in CDDP) to determine RRF and phosphaturia. We compared the balance of phosphate compared with a thrice-weekly hemodialysis considering on phosphate removal: dialysis efficiency, phosphate-binders power on the protein- phosphates intake and the extent of phosphaturia. RESULTS: The patients on infrequent hemodialysis have demonstrated a significant share of urinary phosphate output leading to a weekly phosphoric balance equal to zero or even negative. CONCLUSIONS: The phosphoric balance in infrequent hemodialysis patients is a decisive way to remove the phosphates, confirming that this factor could be decisive on the improved survival and reduced cardiovascular mortality compared to patients receiving thrice-weekly hemodialysis. The Authors stress again the need to keep as long as possible the FRR.

A case report of phosphaturic mesenchymal tumor-induced osteomalacia.

RATIONALE: Tumor-induced osteomalacia (TIO) is a rare and often misdiagnosed syndrome. Surgical resection is currently the first line treatment for TIO. PATIENT CONCERNS: Here we report the case of a 49-year-old woman presented with intermittent pain in the right chest and bilateral hip that had persisted for over two years. DIAGNOSES: She was diagnosed of TIO caused by a phosphaturic mesenchymal tumor based on the following examinations. Laboratory tests revealed high serum alkaline phosphatase, high urinary phosphorus, hypophosphatemia and normal serum calcium levels. 18-FDG PET/CT indicated a systemic multi-site symmetrical pseudo fracture and a tumor in the 7th right rib. INTERVENTIONS: Curettage of the tumor was performed, and pathological analysis also confirmed our diagnoses as a phosphaturic mesenchymal tumor. OUTCOMES: At seven months post-surgery, the symptoms were relieved, proximal muscle strength was improved and serum levels of phosphorus and alkaline phosphatase normalized. The bilateral femoral neck and bilateral pubic bone fractures were blurred in the pelvic plain X-ray, suggesting that the fracture was healing. LESSONS: This case report strengthened the importance of recognition of this rare disease to avoid delay of diagnosis and surgical removal of the causative tumor is recommended.