Severe hypophosphatemic osteomalacia in hormone-refractory prostate cancer metastatic to the skeleton: natural history and pitfalls in management

Clinical performance of a novel chemiluminescent enzyme immunoassay for FGF23

INTRODUCTION

Measurement of fibroblast growth factor 23 (FGF23) has been reported to be clinically useful for the differential diagnosis of chronic hypophosphatemia. However, assays for research use only are available in Japan. Thus, the objective of this study was to examine the clinical utility of a novel and automated chemiluminescent enzyme immunoassay for the measurement of FGF23.

MATERIALS AND METHODS

Participants were recruited from July 2015 to January 2017 at six facilities in Japan. Thirty-eight patients with X-linked hypophosphatemic rickets (XLH 15 males, 23 females, age 0-66 years), five patients with tumour-induced osteomalacia (TIO 3 males, 2 females, age 60-73 years), and twenty-two patients with hypophosphatemia (11 males, 11 females, age 1-75 years) caused due to other factors participated in this study.

RESULTS

With the clinical cut-off value of FGF23 at 30.0 pg/mL indicated in the Diagnostic Guideline of Rickets/Osteomalacia in Japan, the sensitivity and specificity of FGF23-related hypophosphatemic rickets/osteomalacia without vitamin D deficiency (disease group-1) were 100% and 81.8%, respectively, which distinguished it from non-FGF23-related hypophosphatemia (disease group-2). Furthermore, the diagnostic sensitivity of FGF23-related hypophosphatemia with vitamin D deficiency remained at 100%. Among the four patients with FGF23 levels ≥ 30.0 pg/mL in disease group-2, two patients with relatively higher FGF23 values were suspected to have genuine FGF23-related hypophosphatemia, due to the ectopic production of FGF23 in pulmonary and prostate small cell carcinomas.

CONCLUSION

The novel FGF23 assay tested in this study is useful for the differential diagnosis of hypophosphatemic rickets/osteomalacia in a clinical setting.

Mineral metabolism abnormalities in patients with prostate cancer: a systematic case controlled study

PURPOSE

Prostate cancer is the most common tumor in men. To the best of our knowledge a systematic assessment of bone and mineral abnormalities has not been performed in prostatic cancer patients consecutively enrolled.

METHODS

This study was therefore carried out to investigate changes of skeletal and mineral metabolism in patients with prostate cancer (n  = 69). A population of patients with cancer of various origin was also investigated as a control group (n  = 53), since a comparison with non-prostate cancer patients has not been previously reported.

RESULTS

In the prostatic cancer group, one patient had extremely high values of C-terminal Fibroblast Growth Factor 23, low values of tubular reabsorption of phosphate and very high values of bone alkaline phosphatase, suggesting the diagnosis of oncogenic osteomalacia. We found nine patients with primary hyperparathyroidism in the group of prostate cancer vs. only one in cancer patients group (p  <  0.026). We stratified the population on the basis of Gleason score, prostate specific antigen and hormonal therapy. Using a generalized linear model with a logit link to predict the probability of developing primary hyperparathyroidism, only Gleason score, C-terminal fibroblast growth factor 23 and hormonal therapy had a significant effect (p  < 0.05). Controlling for other covariates, a rise in fibroblast growth factor 23 increases the odds of developing primary hyperparathyroidism by 2% (p  = 0.017), while patients with higher values of Gleason score have a much greater probability of developing primary hyperparathyroidism (log-odds  =  3.6, p  <  0.01). The probability decreases with higher values of Gleason score while on hormonal therapy; a further decrease was observed in patients on hormonal treatment and lower values of GS. Finally, lower grade of Gleason score without hormonal therapy have a significant protective factor (p  <  0.01) decreasing the odds of developing primary hyperparathyroidism by 8%.

CONCLUSION

We showed a remarkable prevalence of primary hyperparathyroidism in men with prostate cancer; the multivariate analysis demonstrates that higher aggressiveness of prostate cancer, as determined by Gleason score, is a significant predictor of increased risk of developing primary hyperparathyroidism.

Tumour-associated osteomalacia and hypoglycaemia in a patient with prostate cancer: is Klotho involved?

Tumour-associated osteomalacia is a paraneoplastic syndrome caused by renal phosphate wasting, leading to severe hypophosphataemia. Excess of circulating fibroblast growth factor 23 (FGF23) is the likely cause, acting via the FGF23/α-Klotho coreceptor, a critical regulator of phosphate metabolism. The other possible effects of that complex in humans are still under investigation. We present a case of an 84-year-old Belgian man, presenting prostate cancer with bone metastases. From June 2010 to March 2013, he presented three episodes of disease progression. From January 2012, the patient developed a progressively marked dorsal kyphosis with significant hypophosphataemia. The calculated TRP (tubular reabsorption of phosphate) was decreased and the FGF23 increased. Mid-March 2013, the patient died after a profound unconsciousness due to hypoglycaemia with hypothermia. We hypothesised that the two paraneoplastic manifestations of this patient (tumour-associated osteomalacia and refractory hypoglycaemia) were due to one cause chain with two main nodes-FGF23 and its coreceptor Klotho..

FGF23: mediator of poor prognosis in a sizeable subgroup of patients with castration-resistant prostate cancer presenting with severe hypophosphatemia?

Castration-resistant prostate cancer (CRPC) is an advanced and incurable stage of the second most frequently diagnosed malignancy in men globally. Current treatment options improve survival modestly but eventually fail due to intrinsic or acquired therapeutic resistance. A hypothesis is presented wherein circulating levels of fibroblast growth factor 23 (FGF23), an endocrine member of the fibroblast growth factor family with phosphaturic properties, are proposed as a prognostic and predictive marker to identify CRPC patients with poor prognosis that are amenable to FGF23 antibody therapy (FGF23i) or treatment with fibroblast growth factor receptor inhibitors (FGFRi). With respect to the latter, FGF23 may also serve as a pharmacodynamic marker enabling individualized FGFRi dosing. We recently discovered that the development of severe and sustained hypophosphatemia in CRPC patients undergoing zoledronic acid therapy for bone metastases was associated with markedly worse prognosis compared to patients without or with only mild and transient hypophosphatemia. Severe hypophosphatemia is a typical manifestation of tumor-induced hypophosphatemic osteomalacia (TIO), a paraneoplastic condition mediated by FGF23 overexpression in most instances. While the postulated tumor-promoting role of FGF23 in CRPC or other malignancies has not yet been studied, several lines of evidence suggest that FGF23 may mediate both severe hypophosphatemia (via its endocrine properties) and aggressive CRPC behavior (via autocrine and paracrine activities): (i) FGF23 and the necessary signalling machinery (i.e. members of the fibroblast growth factor receptor [FGFR] family and the essential co-receptor α-KLOTHO [KL]) are highly expressed in a sizeable subgroup of CRPC patients; (ii) FGF/FGFR signalling plays important roles in prostate cancer; (iii) FGF23 can induce its own expression via a positive autocrine feedback loop involving FGFR1; and (iv) this positive feedback loop may be triggered by bone-targeted therapies frequently used for the treatment of CRPC-associated bone metastases. While there is a lack of personalized treatment strategies in the management of CRPC to date, FGF23 targeted therapy has the potential to fill this unmet clinical need in the not-so-distant future. In fact, FGFRi are currently in advanced clinical testing for a number of malignancies such as kidney and lung cancer, but there is a lack of conclusive data on FGFRi therapy in patients selected for FGF/FGFR pathway activation.

Oncogenic osteomalacia -- hypophosphataemic spectrum from "benignancy" to "malignancy"

Though case reports and case series about oncogenic osteomalacia due to benign mesenchymal tumours and much more rarely, secondary to malignant ones exist in the literature, there has not been any series reported from a single department spanning the gamut of causes from benign to malignant. We present 3 patients who were seen at the department of endocrinology of our hospital between 2010 and 2012 with hypophosphataemia and severe skeletal complications. All of them were found to have oncogenic osteomalacia otherwise known as tumour induced osteomalacia (TIO) - a paraneoplastic syndrome characterised by renal phosphate wasting and severe hypophosphataemia. The implicating tumours in our patients ranged from a subcutaneous mesenchymal tumour in the heel to a mixed connective tissue variant within the nasal cavity to metastatic prostate cancer. All our patients had protracted periods before the diagnosis was made, during which time the burden of their metabolic and skeletal pathology had increased. A timely recognition of the clinical features and biochemical findings of this rare but potentially debilitating disease is critical. Physicians should be cognizant of the presence of the disease and its localising and treatment strategies.

Advanced prostate cancer as a cause of oncogenic osteomalacia: an underdiagnosed condition

PURPOSE

Tumor-induced osteomalacia (TIO) is a paraneoplastic bone mineral disturbance related to fibroblast growth factor 23 (FGF23) overproduction by the tumor, usually from mesenchymal origin. Such condition leads to high phosphate renal wasting and, consequently, to cumbersome symptoms as weakness, bone pain, and fractures.

METHOD

Case report.

RESULT

We report a case of an advanced castration-refractory prostate cancer patient, which developed severe hypophosphatemia with elevated phosphate excretion fraction. TIO was suspected, and increased levels of FGF23 reinforced such diagnosis. The patient died 4 months after being diagnosed with TIO.

CONCLUSION

This case suggests that TIO has a dismal prognosis in prostate cancer patients. The clinical oncology community must be aware about such disturbance that can be present in those patients with weakness, bone pain, and hypophosphatemia.

Hypophosphatemia related to paraneoplastic Cushing syndrome in prostate cancer: cure after bilateral adrenalectomy

We report the case of a 71-year-old man with progressive metastatic prostate cancer in whom simultaneous occurrence of paraneoplastic Cushing syndrome (CS) and tumor-induced osteomalacia (TIO) initially was suspected. However, the evolution of biochemical markers of phosphate metabolism during disease course and after bilateral adrenalectomy argued against the diagnosis of TIO. Despite the persistence of progressive prostate cancer, CS and hypophosphatemia resolved in parallel after bilateral adrenalectomy. Thus, these data suggest that paraneoplastic CS per se was involved in the pathogenesis of hypophosphatemia. Calcitriol and intact fibroblast growth factor 23 (FGF23) levels were within the reference range at onset, which is inappropriate in the setting of severe hypophosphatemia. All parameters of phosphate metabolism normalized after resolution of hypercortisolism. Based on the known suppressive effect of glucocorticoids (GCs) on bone remodeling and the inverse relationship between bone turnover rate and circulating FGF23 levels, we postulate that GCs interfere indirectly with phosphate homeostasis by inducing inappropriate FGF23 production and release. This mechanism could further aggravate the hypophosphatemia resulting from GC-induced inhibition of intestinal phosphate absorption. Studies directed at the identification of the molecular pathways in bone mediating the interference of GCs with phosphate metabolism are warranted.

Causes and mechanisms of acid-base and electrolyte abnormalities in cancer patients

Patients with cancer frequently exhibit acid-base and electrolyte disturbances that complicate their management and prolong their hospitalization. The mechanisms encountered for these abnormalities are multifactorial in origin. Both the underlying disease and the therapeutic interventions can contribute to the development of these disturbances. An understanding of the mechanisms involved in their pathogenesis is of paramount importance for their prevention and treatment in cancer patients. This article briefly reviews the causes and the pathophysiology of acid-base and electrolyte abnormalities observed in cancer patients.