Malignancy Hypercalcemia Workup

Malignancy-Associated Hypercalcemia (MAH) — Workup

Use this skill when hypercalcemia is PTH-suppressed and malignancy is on the differential. MAH is usually acute, severe, and a marker of advanced disease.

STEP 1 — Confirm MAH vs. other PTH-independent causes

You should already have:

• Suppressed intact PTH
• Hypercalcemia (often >12 mg/dL with rapid onset)
• Suggestive setting (known cancer, weight loss, advanced disease, pathological fracture)

Order if not yet done:

• PTHrP
• 1,25(OH)2D and 25(OH)D
• SPEP + UPEP + serum free light chains
• CBC, peripheral smear, LDH
• Skeletal imaging — whole-body low-dose CT or PET-CT (more sensitive than bone scan, especially in myeloma)
• TSH, cortisol to exclude endocrine mimics

STEP 2 — Sub-classify MAH

Pattern A — Humoral Hypercalcemia of Malignancy (HHM) — PTHrP elevated, 1,25(OH)2D low/normal, often few or no bone metastases

Typical tumours:

• Squamous cell carcinoma: lung (most common), head & neck, oesophagus, cervix, vulva, skin
• Renal cell carcinoma
• Bladder, ovarian carcinoma
• Less commonly: colon, gastric, prostate, thyroid, non-squamous lung

Biochemistry: hypophosphatemia, low TmP/GFR, increased nephrogenous cAMP — mimics PTH action.

Action: search for the primary with imaging guided by symptoms (CT chest/abdomen/pelvis, ENT review for head & neck SCC, dermatologic exam, urine cytology). PTHrP can be tracked as a tumour marker once the diagnosis is established.

Pattern B — Solid tumour with skeletal metastases + elevated PTHrP (mixed mechanism)

Typical: breast cancer, prostate (rarely), other osteolytic mets.

Mechanism: PTHrP from tumour both raises systemic calcium and drives local osteolysis (RANKL ↑, OPG ↓, TGF-β feedback loop).

Action: confirm bone metastases (CT, bone scan, MRI as needed). Treat as MAH plus bone-targeted therapy.

Pattern C — Hematologic malignancy with elevated 1,25(OH)2D — lymphoma pattern

Typical: non-Hodgkin lymphoma, Hodgkin lymphoma.

Mechanism: extrarenal 1α-hydroxylase in tumour tissue. PTHrP may also be elevated in some cases.

Action: confirm lymphoma — LDH, lymph node biopsy, PET-CT, bone marrow if suspected. Glucocorticoids are particularly effective here (suppress 1α-hydroxylase + tumour activity).

Pattern D — Ectopic PTH secretion — PTH itself elevated (not PTHrP) in a non-parathyroid tumour

Rare. Documented tumours: ovarian, lung, thyroid, thymus, gastric.

Suspicion arises when imaging fails to identify a parathyroid adenoma despite biochemically PTH-dependent hypercalcemia. Confirm with tumour-tissue PTH immunostaining or molecular studies in selected cases.

Action: surgical removal of the primary if feasible.

Pattern E — Multiple myeloma — SPEP/UPEP positive, light chains elevated

Mechanism: bone-resorbing factors (MIP-1α, IL-6, RANKL ↑, OPG ↓, DKK-1, sclerostin). PTHrP rarely elevated.

Key clinical features:

• Hypercalcemia in ~30% of myeloma patients
• Often coexists with renal failure (Bence-Jones nephropathy, light-chain cast nephropathy) → so unlike other MAH, expect hyperphosphatemia, not hypophosphatemia
• ALP usually normal (no osteoblastic activity); bone scans frequently negative
• Bone pain in 80%, pathological fractures common

Action:

• Confirm: bone marrow biopsy, FISH (del17p, t(4;14), t(14;16), 1q gain, t(11;14)), whole-body low-dose CT or PET-CT.
• Bisphosphonates have a dual benefit — control hypercalcemia AND reduce skeletal events / tumour burden.
• See the mm-diagnostic-workup skill for the full myeloma workup.

STEP 3 — Decide treatment direction

Two parallel tracks:

Track 1 — Treat the hypercalcemia (use acute-hypercalcemia-management skill if Ca >12 with symptoms or >14):

• Hydration (NS), then antiresorptive (denosumab 120 mg SC, or zoledronic acid 4 mg IV, or pamidronate 60–90 mg IV).
• Glucocorticoids are particularly effective in lymphoma, myeloma, and granulomatous-pattern (1,25(OH)2D-driven) MAH.
• Calcitonin (4–8 IU/kg SC/IM q6–12h) for first 48–72 h while waiting for antiresorptive to take effect.

Track 2 — Treat the underlying cancer — definitive control of MAH requires reducing tumour burden. Without this, hypercalcemia recurs rapidly.

Track PTHrP after treatment:

• PTHrP does not fall with hypercalcemia treatment.
• PTHrP does fall with successful tumour reduction → useful as a tumour marker on follow-up.

CLINICAL GUARDRAILS

• MAH = advanced disease. Patients with new-onset MAH have a poor prognosis; involve oncology and palliative care early.
• Bone scan misses myeloma. Use whole-body low-dose CT or PET-CT.
• Hyperphosphatemia + hypercalcemia + suppressed PTH → think myeloma with renal failure, not HHM.
• Glucocorticoids are not first-line for HHM (they don't work) but ARE effective for lymphoma, myeloma, and granulomatous causes.
• Bisphosphonates need dose adjustment in renal impairment — denosumab is preferred when CrCl <30 mL/min (no renal clearance).
• Watch for hypocalcemia after antiresorptive in vitamin D-deficient patients — correct 25(OH)D first if low.
• PTHrP can be elevated in normocalcemic cancer patients — significance unclear; do not use in isolation to diagnose MAH.

SOURCE

Bilezikian JP, Endotext. Approach to Hypercalcemia. NCBI Bookshelf NBK279129. Section: Malignancy-Associated Hypercalcemia (HHM, MAH with skeletal metastases, hematologic malignancies, ectopic hyperparathyroidism, multiple myeloma).