THOUSAND OAKS, Calif. (AP) — Amgen Inc. said Monday the Food and Drug Administration wants more information about its osteoporosis treatment Prolia before granting marketing approval. It delays a drug seen as a potential blockbuster for the company. In a letter, the FDA said it wants to know how Amgen will monitor patients who use Prolia, and wants the company to develop a strategy to evaluate the risks of the drug, Amgen said. In premarket trading, Amgen shares fell $1.38, or 2.3 percent, to $59.94. The company wants to market Prolia for the prevention and treatment of postmenopausal osteoporosis. The FDA said Amgen needs to run more clinical tests of Prolia as a preventive therapy, but Amgen will not have to perform further testing of Prolia as a treatment for the illness. Prolia, which is also called denosumab, works by targeting cells that break down bone. Amgen said it is reviewing the FDA's message, called a complete response letter, and plans to respond soon. The company is also seeking approval for Prolia in bone loss caused by hormone deprivation therapy, which is used as a treatment for prostate and breast cancer. It expects a separate FDA response to that application. Amgen is also seeking regulatory approval for Prolia in the European Union, Switzerland, Australia, and Canada. It is testing the drug against other disease that can cause bone loss, such as rheumatoid arthritis, as well as cancers that can spread to or damage bones.