A patient with cancer, hyperparathyroidism, and hyperkalemia — what is the most likely cause of the hyperkalemia?

Hyperparathyroidism's primary metabolic effect is on calcium and phosphate (causing hypercalcemia), not potassium — it is not a direct, expected cause of hyperkalemia. The underlying malignancy (through mechanisms like tumor lysis, paraneoplastic effects, or renal involvement) is the most plausible explanation for hyperkalemia among the choices given.