The differentiation of primary hyperparathyroidism from the hypercalcemia of malignancy.

The presence of hypercalcemia in patients with known cancers may be due to the cancers themselves, or to co-existing primary hyperparathyroidism. The differentiation of primary hyperparathyroidism from the hypercalcemia of malignancy is important since the relief of distressing symptoms and prevention of hypercalcemic crises and renal failure can be accomplished relatively easily by parathyroid surgery in the former condition, and only with difficulty, at times, with fluids and drugs in the latter condition. The histories of three recent patients are presented, which demonstrate the difficulties inherent in the differentiation of these conditions. These patients were ultimately found at operation to have primary hyperparathyroidism in addition to malignancies of the cervix, adrenal gland and kidney. In our experience the following have been helpful in establishing a diagnosis; history of hypercalcemia prior to development of cancer, the type of cancer itself, the effect of cancer therapy on the hypercalcemia, and selective venous sampling with radioimmunoassay for parathyroid hormone.