Effect of tamoxifen on serum lipid metabolism.

The effect of tamoxifen, an antiestrogenic agent, on lipid metabolism was studied in postmenopausal patients with breast cancer who received the drug for postoperative adjuvant treatment following mastectomy. To measure total cholesterol and triglyceride concentrations, fasting blood samples were collected before and 2 months after the initiation of tamoxifen therapy from 16 patients who satisfied the study criteria. All patients were normolipidemic before tamoxifen was administered. Control samples were obtained from hypertriglyceridemia patients who were free from breast cancer. Marked hypertriglyceridemia was observed in 3 of 16 patients after tamoxifen treatment. The activity of lipoprotein lipase and hepatic triglyceride lipase, the key enzymes of triglyceride metabolism, decreased significantly in all of 16 patients as a result of tamoxifen treatment (P = 0.008 and P = 0.007, respectively). However, the mean mass of lipoprotein lipase significantly increased (P = 0.011) after tamoxifen treatment. We therefore conclude that tamoxifen might increase inactive lipoprotein lipase. Because marked hyperlipidemia is a potent risk factor for life-threatening acute pancreatitis and arteriosclerosis, plasma lipid levels should be tested periodically during tamoxifen treatment, even if the patients are normolipidemic during the pretreatment stage.