What is a common cause of hypercalcemia associated with elevated calcium levels and low parathyroid hormone (PTH) levels?

Hypercalcemia with elevated calcium levels and low parathyroid hormone (PTH) levels is commonly seen in malignancy. This condition often arises due to the effects of cancer on calcium metabolism, most notably through mechanisms such as the secretion of parathyroid hormone-related peptide (PTHrP) by certain tumors, which mimics the action of PTH and leads to increased calcium release from bone and renal reabsorption of calcium.

In the context of malignancy, cancer cells can produce substances that stimulate osteoclastic activity, leading to bone resorption, or can directly stimulate renal tubular reabsorption of calcium. Since the calcium levels are elevated, the body senses this and consequently suppresses PTH secretion, resulting in low PTH levels.

Other causes, like kidney failure, renal tubular acidosis, and primary hyperparathyroidism, would typically present with different levels of calcium and PTH. For instance, in primary hyperparathyroidism, one would expect elevated levels of both calcium and PTH due to the overactivity of the parathyroid glands. Understanding these relationships helps to distinguish malignancy as the leading cause of hypercalcemia with specifically low PTH levels.