Primary lung cancer starts in the cells of the lung. The lungs are in the chest, one on each side of the heart. The right lung has 3 main parts, called lobes. The left lung is a bit smaller and has 2 lobes. The lungs are cushioned and protected by a thin covering called the pleura. The pleura has 2 layers of tissue. One layer covers the lungs and the other lines the inside wall of the chest. There is a small amount of fluid (pleural fluid) between the 2 layers of the pleura. The pleural fluid allows the layers to slide over each other as you breathe.
You use your lungs when you breathe. The air you take in through your nose or mouth flows down the trachea (windpipe). The trachea divides into 2 tubes called the left and right bronchi, which carry air to each lung. Once inside the lung, the bronchi divide into smaller and smaller tubes called bronchioles. Each bronchiole ends in a cluster of tiny air sacs called alveoli. The alveoli take oxygen from the air you breathe in and pass it into the blood, which circulates it to all parts of your body. The alveoli also remove carbon dioxide from the blood, which is pushed out of the lungs when you exhale.
The 2 main types of lung cancer are:
- Non–small cell lung cancer (NSCLC) is the most common type of lung cancer. It grows more slowly than small cell lung cancer.
- Small cell lung cancer (SCLC) grows quickly and often spreads to distant parts of the body.
Each type of lung cancer behaves quite differently, so they are treated differently.
Cancer that starts in another part of the body and spreads to the lung (lung metastasis) is not the same disease as cancer that starts in the lung (primary lung cancer). Almost any type of cancer can spread to the lung.
A rare type of cancer called pleural mesothelioma is often mistakenly called a lung cancer. But pleural mesothelioma starts in the lining of the lung and is very different from cancer that starts in the lung.