Every year, roughly 230,000 people are diagnosed with lung cancer, making it the second most common cancer in men and women, according to the National Cancer Institute. While that seems high, the number of people diagnosed with the disease has been declining over the last 10 years. The exception: The rate of lung cancer found in never-smokers—adults who’ve smoked fewer than 100 cigarettes in their lifetime—has increased.

“We've seen a bump in these patients over the past couple of years,” says Benjamin P. Levy, M.D., a thoracic medical oncologist and clinical director of medical oncology at Johns Hopkins Sidney Kimmel Cancer Center in Washington, D.C. Lung cancer in never-smokers now accounts for 15% to 20% of all cases, he adds. And while no one knows for sure why there’s been an uptick, researchers have identified some possible links and special considerations to be aware of if you or a family member has been diagnosed.