**Core Concept**
Hypercalcemia of malignancy is a condition where elevated serum calcium levels are caused by the production of parathyroid hormone-related protein (PTHrP) or other factors by cancer cells. This can lead to various complications, including renal impairment, bone pain, and increased risk of fractures.

**Why the Correct Answer is Right**
The patient's symptoms, including intermittent epistaxis, fatigue, and bone pain, are consistent with hypercalcemia of malignancy. The elevated serum calcium level of 12 mg/dL is also indicative of this condition. The production of PTHrP by cancer cells can lead to increased bone resorption, resulting in bone pain and increased risk of fractures. Additionally, renal impairment can occur due to the high calcium levels, leading to symptoms such as fatigue and epistaxis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the patient's symptoms and laboratory findings.
**Option B:** This option is not a direct complication of hypercalcemia of malignancy.
**Option C:** This option is not a direct complication of hypercalcemia of malignancy.

**Clinical Pearl / High-Yield Fact**
In patients with hypercalcemia of malignancy, it is essential to investigate for underlying malignancy, as prompt treatment can prevent further complications. Common malignancies associated with hypercalcemia include breast cancer, lung cancer, and multiple myeloma.

**Correct Answer: C. Nephrolithiasis.**