Two Cases of Primary Hyperparathyroidism Associated with Colon Cancer

Hypercalcemia is often observed in cancer patients secondary to parathyroid hormone (PTH) related peptide production. However, primary hyperparathyroidism and colon cancer rarely present simultaneously. Calcium is believed to have a chemopreventive effect against colorectal cancer because it reduces crypt cell hyperproliferation in both humans and in animals. There is evidence to suggest that the incidence of colorectal cancer in humans is reduced by high calcium intake. In patients with primary hyperparathyroidism, increased PTH activates 1,25(OH)2D and enhances calcium absorption in the gut. Consequently, the calcium level in the lumen is decreased, leading to an elevated risk of colorectal cancer. We report two patients with colon cancer and hypercalcemia secondary to primary hyperparathyroidism, along with a brief review of the literature. (J Korean Endocr Soc 23:204~209, 2008)