Today, Pfizer Inc. announced that US health regulators approved the first drug to treat a rare, progressive lung disease.

The company said that the US Food and Drug Administration (FDA) approved its Rapamune (sirolimus) for the treatment of lymphangioleiomyomatosis (LAM), a rare, progressive disease that affects the lungs, kidneys and the lymphatic system.

The disease impacts mainly women of childbearing age and has an incidence rate of just two to five out of every million women globally. The disease can result in abnormal growth of smooth muscle cells in the lung. Over time, the muscle growth can cause airway obstructions and limit the delivery of oxygen to the body. There are currently 800 patients in the US diagnosed with LAM, a disease that is often fatal.

“Pfizer is proud to gain approval for Rapamune as the first treatment for patients with LAM, through our work with the FDA, the clinical investigation team and the LAM Foundation,” said Rory O’Connor, MD, senior vice president and head of Global Medical Affairs, Global Innovative Pharmaceuticals Business, Pfizer Inc. “This type of cooperative effort creates opportunities for innovation in developing therapies for patients with rare diseases.”

Rapamune is an immunosuppressive agent. In addition to being approved for LAM, the drug is approved for the prophylaxis of organ rejection in patients 13 years and older receiving kidney transplants.

The agency’s approval is based on the results from the MILES Trial, which included 89 LAM patients with moderate lung impairment and showed that those receiving Rapamune for one year experienced stabilization of lung function as measured by forced expiratory volume in one second (FEV1).  Adverse events were consistent with the known safety profile for Rapamune in patients with renal transplants, with the addition of weight decrease.

“This approval is a landmark breakthrough for LAM patients to have access to this important treatment option,” said Susan E. Sherman, executive director of the LAM Foundation. “It is the result of decades of work by researchers and women of the LAM community who volunteered for this pivotal clinical trial.”