genetic and or hereditary. one of my friends passed away some years ago from lung cancer. he was never a smoker nor working in harsh (air) conditions. his grandpa, father, uncle, brother, cousins also suffered from the same cancer and passed away. in his case, it only afflicted male members of his family and was late adult-onset, which meant they were clueless about it until they hit past 50. not sure if females are carriers but do not succumb to the disorder, but so far all females in his family have never succumb to the same cancer.