**Core Concept**
Immediate treatment of hypercalcemia of malignancy involves correcting the volume depletion and improving renal function to reduce calcium levels. This is crucial in managing severe hypercalcemia, which can cause life-threatening complications.

**Why the Correct Answer is Right**
IV fluids are the first line of treatment in hypercalcemia of malignancy, as most patients have underlying volume depletion due to vomiting, diarrhea, or renal losses. Administering IV fluids helps to replenish the volume, improve cardiac output, and increase renal blood flow, thereby enhancing the excretion of calcium. This is particularly important in the initial management of severe hypercalcemia, as it can help to rapidly reduce calcium levels and improve symptoms.

**Why Each Wrong Option is Incorrect**
**Option B:** Bisphosphonates, such as zoledronic acid, are effective in reducing bone resorption and calcium levels, but they are not the immediate treatment of choice. They are usually administered after initial hydration and stabilization of the patient.
**Option C:** Calcitonin can also help to reduce calcium levels by inhibiting osteoclast activity and increasing calcium excretion. However, its use is typically reserved for patients who are not responding to IV fluids or have severe, life-threatening hypercalcemia.
**Option D:** Glucocorticoids, such as prednisone, can help to reduce hypercalcemia by inhibiting osteoclast activity and increasing urinary calcium excretion. However, they are not typically used as first-line treatment and are more effective in patients with hypercalcemia due to sarcoidosis, vitamin D toxicity, or other non-malignant causes.

**Clinical Pearl / High-Yield Fact**
In patients with hypercalcemia of malignancy, it is essential to address the underlying cause, such as bony metastases or paraneoplastic syndromes, in addition to treating the hypercalcemia itself. This may involve administering bisphosphonates, calcitonin, or other agents to reduce bone resorption and calcium levels.

**✓ Correct Answer: A. IV fluids. IV fluids are the immediate treatment of choice for hypercalcemia of malignancy, as they help to correct volume depletion and improve renal function.**