One of the hardest truths about lung cancer is that so many people who've kicked the smoking habit will still develop lung cancer. "Half the lung cancer cases in the United States are people who are former smokers," said Paul Bunn Jr., MD, executive director of the International Association for the Study of Lung Cancer.Bunn, who is also a researcher at the University of Colorado Cancer Center, spoke April 2 at a press conference during the annual meeting of the American Association for Cancer Research in Orlando.Lung cancer is the leading cause of cancer death in men and women in the U.S., as well as the leading cause of cancer death worldwide. The five-year survival rate is 15 percent because patients often present with late-stage disease that is not treatable by current therapies.Although people who quit smoking remain at risk of developing lung cancer, "we need to repair their lungs through chemoprevention," Bunn said.Bunn presented an update on a multicenter, double-blind, placebo-controlled phase 2 study that tested the effect of iloprost, used primarily to treat pulmonary arterial hypertension, on 152 former smokers who had endobronchial dysplasia. Iloprost is similar to a hormone called prostacyclin, which is produced in the lungs and keeps the blood vessels relaxed, according to mayoclinic.com. Most patients with non-small cell lung cancer (NSCLC) have decreased levels of prostacyclin. A pre-clinical study using transgenic mice exposed to cigarette smoke showed that iloprost prevented lung cancer.Bunn said results of the current study were significant because they identified a biomarker for measuring the success of lung cancer chemoprevention.