According to the global pharmaceutical company, Pfizer, the U.S. FDA approved its rapamune (sirolimus) for the treatment of lymphangioleiomyomatosis (LAM). LAM is a rare, progressive disease that affects the lungs, the kidneys and the lymphatic system, and it affects women predominantly. It manifests pathologically as an overgrowth of abnormal smooth muscle-like cells in the lungs, resulting in the formation of lung cysts and the destruction of normal lung tissue. Mutation in TSC1 or TSC2 gene is responsible for LAM. Without lung transplantation, many patients would progress to lung failure. Rapamune is an immunosuppressive agent previously approved for the prophylaxis of organ rejection in kidney transplant patients and the FDA originally granted it Orphan Drug Designation in October, 2012. Its efficacy is demonstrated in a multicenter international clinical trial. This FDA approval makes rapamune the first approved treatment for LAM.