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Mechanism of hypercalcemia in HL has long been suggested to involve extra-renal activation of 1α-hydroxylase leading to production of 1, 25(OD)2 Vitamin D3 or Calcitriol, an active metabolite of Vitamin D, which leads to increased re-absorption of calcium and phosphate from intestine, increased osteoclast activation and bone resorption as well as increased phosphate re-absorption in renal tubules

Hypercalcemia of malignancy involves three mechanisms: 1. Humoral hypercalcemia mediated by PTHrP—seen in solid tumors like breast cancer and adult T cell leukemia/lymphoma (ATLL), 2. Direct osteoclast mediated bone resorption due to bony metastasis—seen in solid tumors and multiple myeloma, 3. Calcitriol mediated hypercalcemia—seen in Hodgkin’s and non-Hodgkin’s lymphoma as well as granulomatous disorders like tuberculosis, sarcoidosis, leprosy and disseminated Candidiasis

Hypercalcemia in HL is rare and its incidence has been reported as 0.9, 1.6 and 5.4 % in different series

The source of 1α-hydroxylase in HL has been postulated as monocytes and macrophages infiltrating the tumor akin to tuberculosis or sarcoidosis and is stimulated by IFN-γ secreted by T-lymphocytes

Like sarcoidosis, patients with HL exhibit increased sensitivity to Vitamin D supplements and sunlight, which have been found to precipitate hypercalcemia in these patients

Classical biochemical profile in Calcitriol mediated hypercalcemia include: an elevated calcium, normal/slightly elevated phosphate, normal 25(OH) Vitamin D, suppressed PTHrP and PTH, elevated Calcitriol and a normal/increased tubular reabsorption of phosphate

not been associated with a poorer prognosis and tends to subside after treatment of the underlying disease

Humoral hypercalcemia is predominant in squamous cell, renal cell and ovarian cancers, and lymphomas are associated with 1,25-dihydroxyvitamin D mediated hypercalcemia

20% of cases of hypercalcemia of malignancy and is frequently encountered in multiple myeloma, metastatic breast cancer, and to a lesser extent in leukemia and lymphoma

Physiologic bone turnover requires the complementary activity of osteoblasts – mesenchymal stem cell-derived bone-forming cells – and bone-resorbing cells of monocyte and macrophage lineage known as osteoclasts

In local osteolytic hypercalcemia, the RANKL/RANK interaction results in excessive osteoclast activation leading to enhanced bone resorption and thus hypercalcemia

In addition, osteoclast activation is also mediated by malignancy secreted cytokines, including interleukin-1, initially termed “osteoclast stimulating factor”

Macrophage inflammation protein 1-alpha (MIP 1-alpha)

hypercalcemia is through extra-renal 1,25-dihydroxyvitamin D (calcitriol) production

1% of cases

increased production of 1,25-dihydroxyvitamin D occurs nearly exclusively in Hodgkin and non-Hodgkin lymphoma with case reports of the same in ovarian dysgerminoma

1-α-hydroxylase in the kidney, a process regulated by PTH

in 1,25-dihydroxyvitamin D induced hypercalcemia, malignant cells likely recruit and induce adjacent macrophages to express 1-α-hydroxylase, converting endogenous calcidiol into calcitriol.31 Calcitriol then binds to receptors in the intestine leading to heightened enteric calcium reabsorption with resultant hypercalcemia

this mechanism of disease is best conceptualized as an absorptive form of hypercalcemia

Ectopic production of PTH by malignant cells has been described in a handful of cases involving cancer of the ovary and lung, as well as neuroendocrine tumors and sarcoma

primary hyperparathyroidism and malignancy comprising nearly 90% of cases of hypercalcemia

an initial panel consisting of PTH, PTHrP, phosphorus, 25-hydroxyvitamin D, and 1,25-dihydroxyvitamin D should be obtained

Lymphoma, a hypercalcemia due to 1,25-dihydroxyvitamin D mediated pathways, is implied by elevations in 1,25-dihydroxyvitamin D without concomitant elevations in 25-hydroxyvitamin D. In such cases, PTH is low and PTHrP undetectable

Treatment of hypercalcemia of malignancy is aimed at lowering the serum calcium concentration by targeting the underlying disease, specifically by inhibiting bone resorption, increasing urinary calcium excretion, and to a lesser extent by decreasing intestinal calcium absorption

mildly symptomatic disease

marked symptoms

hydration with isotonic fluid (if admitted), avoidance of thiazide diuretics, and a low-calcium diet

denosumab

Denosumab is an RANKL antibody that inhibits osteoclast maturation, activation, and function