Uncontrolled cell division in your lungs is what causes lung cancer. It is a normal part of your cells' function to divide and create more copies of them. But occasionally, they undergo changes (mutations) that lead them to continue producing more of themselves when they shouldn't. Your organs eventually develop tumors from damaged cells that continue to divide uncontrollably and form tissue masses.

The term "lung cancer" refers to cancers that begin in your lungs, most commonly in the bronchi or bronchioles or small air sacs (alveoli). It's customary to refer to cancers that originate elsewhere and spread to your lungs by their original location (your healthcare provider might use the term "cancer that is metastatic to your lungs" instead).