Hypophosphatemia in cancer patients

Abstract

Dysregulation of phosphorus homeostasis resulting in hypophosphatemia is common in cancer patients and can result in serious complications and impact outcomes. Several factors, including critical illness, nutritional status, cancer type and therapy, influence the development of hypophosphatemia. Hypophosphatemia can develop as a result of phosphaturic mesenchymal tumors or as a paraneoplastic phenomenon. The clinical presentation for hypophosphatemia varies depending on the duration and severity of the hypophosphatemia and affects several organ systems. Among other serious effects, hypophosphatemia can impair tissue oxygenation and can cause hemolysis, leukocyte and platelet dysfunction, encephalopathy, seizures, arrhythmias, cardiomyopathy, rhabdomyolysis and coma. Multiple studies have demonstrated that hypophosphatemia is an adverse prognostic marker in inpatients with increased in-hospital stay, mortality and postoperative complications. The phosphate level is homeostatically regulated and maintained in a narrow range by three main hormones: parathyroid hormone, fibroblast growth factor 23 and 1,25-dihydroxyvitaminD₃. Together, these hormones regulate how the intestine, kidneys and bones traffic phosphorus. Several hematological malignancies and cancer therapies are associated with proximal tubular dysfunction (Fanconi syndrome), resulting in phosphaturia. Caution should be taken with parenteral administration of phosphate salts, because secondary complications can develop, principally due to hypocalcemia. The general approach to hypophosphatemia should target the underlying cause. Early recognition and prevention are essential and the approach to hypophosphatemia in the cancer patient, because of the nuances and complexity, should be multidisciplinary.

Keywords: Fanconi syndrome; electrolytes; hypophosphatemia; onconephrology; phosphate; phosphaturia; phosphorus.

FIGURE 1:

Quantitative aspects of phosphorus homeostasis in humans [21]. Factors that can cause hypophosphatemia are in red.

FIGURE 2:

Mechanism for phosphate reabsorption in the proximal tubule in the kidney. Significant absorption occurs in the proximal tubule (85%) and ascending limb of the loop of Henle/distal convoluted tubule (15%). A⁻, organic anion.

FIGURE 3:

Diagnostic approach to hypophosphatemia. FEPO₄, fractional excretion of phosphate; 24-h UPO₄, 24-h urine PO₄; N, normal level; $\uparrow ,\mathrm{ }\mathrm{increased};\downarrow ,$ decreased.