High Calcium in Breast Cancer: What It Means and What to Do

High blood calcium (hypercalcemia) can occur in people with breast cancer for a few different reasons, and its importance depends on the level, speed of rise, and symptoms. It often relates to bone involvement or cancer-related changes in bone turnover, but it can also be due to other medical conditions or medications. It’s reasonable to be concerned, but there are effective, well‑established treatments and clear steps to evaluate the cause.

Why calcium can be high

• Bone metastases and osteolysis: Breast cancer commonly spreads to bone, where tumor activity can increase bone breakdown and release calcium into the bloodstream, leading to hypercalcemia. This process is a known “skeletal-related event” in breast cancer. [PM9] [PM20]
• Cancer-mediated factors: Some tumors release proteins (like PTHrP) that raise calcium by acting like parathyroid hormone, increasing bone resorption and kidney calcium retention. This mechanism is a major cause of malignancy-related hypercalcemia. ^[1]
• Medications or hormonal therapies: Certain androgen therapies historically used in breast cancer can stimulate bone breakdown and cause hypercalcemia; stopping the drug is advised if this occurs. ^{[2] [3] [4]}
• Non-cancer causes: Overactive parathyroid glands (primary hyperparathyroidism), excess vitamin D or calcium intake, kidney problems, granulomatous diseases, or prolonged immobilization can also raise calcium. These need to be checked because they are managed differently. ^{[5] [6] [7]}

What symptoms to watch for

Hypercalcemia ranges from silent to life‑threatening; symptoms typically correlate with how high and how fast calcium rises. Common signs include nausea, vomiting, constipation, dehydration with intense thirst and frequent urination, confusion or drowsiness, and sometimes heart rhythm changes and bone pain. If you develop severe fatigue, mental status changes, or worsening dehydration, seek urgent care. ^{[8] [9]}

How doctors evaluate high calcium

When calcium is elevated, clinicians confirm the level (including “corrected” calcium if albumin is low) and look for the cause. Typical tests include serum calcium (and/or ionized calcium), parathyroid hormone (PTH), PTHrP, vitamin D, kidney function, and urine calcium. Imaging of bones (or other sites) may be considered to look for metastases. Pinpointing the cause guides treatment and helps predict risk. ^{[1] [7] [10]}

Why this matters for prognosis

Bone metastasis with skeletal-related events such as hypercalcemia signals more advanced disease and is linked with higher morbidity. In large datasets, breast cancer with bone metastases has worse survival, and having skeletal-related events further worsens prognosis compared with those without these events. That said, appropriate systemic therapy and supportive measures can improve outcomes and quality of life. [PM31] [PM9]

Malignancy-related hypercalcemia across solid tumors is generally a marker of poor prognosis; however, selected patients who receive effective systemic cancer therapy after an episode have longer survival than those who do not. Controlling the cancer and correcting calcium can change the trajectory for some individuals. [PM32]

How hypercalcemia is treated

Treatment depends on severity and cause, and often proceeds in steps:

• Immediate measures for moderate–severe cases:
  • Intravenous fluids to correct dehydration and help the kidneys flush calcium. ^[11]
  • Anti-resorptive therapy to slow bone breakdown:
    • IV bisphosphonates (e.g., zoledronic acid, pamidronate) are a cornerstone; they reduce skeletal complications and help lower calcium. [PM11] [PM22]
    • Denosumab (a RANKL antibody) is at least as effective, and in several analyses reduces skeletal-related events more than zoledronic acid and can be favored in kidney impairment. [PM21] [PM20]
• Address the underlying driver:
  • If bone metastases are present, ongoing antiresorptive therapy plus effective systemic cancer treatment (endocrine therapy, chemotherapy, targeted therapy) is important to prevent further events and improve quality of life. [PM9] [PM20]
  • If a drug is causing hypercalcemia (e.g., certain androgens), discontinuation is advised. ^{[2] [3] [4]}
  • If primary hyperparathyroidism or other non-cancer causes are found, targeted endocrine management is pursued. Tailored therapy hinges on the confirmed cause. ^[12]

Modern bone-directed care in breast cancer

• Bisphosphonates: Reduce the risk of fractures, spinal compression, and hypercalcemia; zoledronic acid is potent and widely used from the first diagnosis of bone metastasis. They are a standard component of care for bone involvement. [PM11] [PM22]
• Denosumab: Shown to reduce skeletal-related events more than zoledronic acid in some trials and meta-analyses, with different side-effect profiles; useful especially when kidney function limits bisphosphonates. Clinicians balance benefits, risks, and preferences. [PM21] [PM20]
• Other modalities: Radiation to painful sites, surgery for impending or actual fractures, and radiopharmaceuticals can be added based on symptoms, location, and overall health. A multidisciplinary plan is common. [PM19] [PM20]

Practical steps you can take

• If you’ve been told your calcium is high, ask your team about the exact number, whether it’s “mild” or “severe,” and what’s believed to be causing it. Clarifying the cause is key to the right treatment. ^[7]
• Share all medications and supplements (including vitamin D and calcium) with your team; dosing may need adjustment. Some over-the-counter products can worsen hypercalcemia. ^[9]
• Report new or worsening symptoms promptly especially confusion, severe thirst, constipation, or vomiting since these may indicate a more urgent problem. Early action helps prevent complications. ^[8]
• Discuss bone-protective therapy if you have bone metastases; ask about bisphosphonates versus denosumab, dental checks to reduce jaw osteonecrosis risk, and kidney monitoring. These therapies meaningfully reduce skeletal events and improve comfort. [PM11] [PM21]

Bottom line

High calcium in someone with breast cancer can be due to cancer activity in bone, tumor-related hormonal signals, medications, or unrelated endocrine issues. While it can signal advanced disease and requires attention, it is commonly manageable with hydration, bone-targeted drugs, and effective cancer therapy, and identifying the exact cause guides the best plan. [PM9] [PM20] ^[11]