Ashley Rivas was 26 when she noticed she was getting tired earlier than usual on her runs. Over the next few years, the X-ray technician from Albuquerque, New Mexico, developed a persistent cough and wheezing, which her doctors attributed to exercise-induced asthma. She had other symptoms, too: weight loss, fever, and several bouts of pneumonia. Still, when Rivas finally decided to perform a chest X-ray on herself, cancer was the last thing on her mind. The image revealed a mass on her right lung that turned out to be a malignant tumor. Rivas was 32 and had never smoked a cigarette in her life. "I want people to know lung cancer can happen to anyone," she says. Lung Association spokesperson Andrea McKee, MD, the chair of radiation oncology at Lahey Hospital Medical Center in Burlington, Massachusetts. "Having said that, 15% of patients diagnosed with lung cancer have no history of tobacco use -- and they may be quite young." Other known risk factors aside from smoking include a family history of the disease, as well as exposure to certain air pollutants, such as asbestos, arsenic, radon, even diesel fumes, says Dr. McKee. Lung cancer is the most common cancer worldwide; and each year, it kills more women than breast, ovarian, and uterine cancer combined. 25 Breast Cancer Myths Busted If it's diagnosed early, the disease is actually highly curable, Dr. McKee says. Luckily this was the case for Rivas. She had her tumor removed in 2013, and is now thriving. (She ran a half-marathon last year!) But only about 16% of cases are caught at stage 1. "Usually it's like a 7- to 8-millimeter nodule sitting in the middle of a lung that doesn't have any symptoms associated with it," says Dr. McKee. Most patients are diagnosed later, once the tumor has grown large enough that it's "pushing on an airway, resulting in some breathing problems," she explains. So when should you get a lingering cough checked out? "To be safe, I would say that any cough that you're concerned about that's persisting beyond a few weeks, you should talk with your doctor," says Dr. McKee. "A cough shouldn't linger beyond two or three weeks."