Calcium and Parathyroid USMLE Step 1 Practice Question
A 71-year-old man with metastatic breast cancer presents with severe hypercalcemia (14.2 mg/dL), anemia, and renal dysfunction (creatinine 2.8 mg/dL). Vital signs show BP 138/82, HR 98, RR 20, temperature 37.2°C, and SpO2 98% on room air. PTH is suppressed at 12 pg/mL (normal 15-65). Phosphate is elevated at 5.1 mg/dL. Chest X-ray confirms multiple pulmonary metastases. He denies recent thiazide use. Which of the following is the primary mechanism of hypercalcemia in this patient?
Answer choices
- AProduction of calcitriol by malignant cells
- BPTHrP secretion by cancer cells stimulating osteoclast-mediated bone resorptionCorrect answer
- CDirect invasion of bone by metastatic cancer producing osteolytic factors
- DIncreased renal 1α-hydroxylase activity independent of PTH
- EReduced renal calcium excretion from acute kidney injury alone
- FEctopic parathyroid hormone production by neuroendocrine tumor cells
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.