Which cancer is most likely to cause paraneoplastic hypercalcemia?

Paraneoplastic hypercalcemia is commonly associated with certain types of malignancies that produce parathyroid hormone-related peptide (PTHrP) or other factors that mimic parathyroid hormone, leading to increased calcium levels in the bloodstream. Small cell lung cancer (SCLC) is well-known for this phenomenon, primarily because it frequently secretes PTHrP, which triggers bone resorption and increases calcium reabsorption in the kidneys, resulting in hypercalcemia.

While breast cancer and renal cell carcinoma can also cause hypercalcemia, they typically do so through different mechanisms or are less common in their association compared to SCLC. Renal cell carcinoma, for example, can lead to hypercalcemia due to local osteolytic metastases or through a separate process related to increased renal absorption. Thyroid carcinoma is generally not associated with hypercalcemia.

Thus, small cell lung cancer stands out as the cancer most likely to induce paraneoplastic hypercalcemia, making it the best choice in this context.