Interior of the cecum and lower end of ascending colon with the ileocecal valve labeled as colic valve. Endoscopic image of cecum with arrow pointing to ileocecal valve in foreground.
Lung cancer is a malignant tumour that starts in the cells of the lung. Malignant means that it can spread, or metastasize, to other parts of the body. When cancer starts in lung cells, it is called primary lung cancer. The lung is part of the respiratory system. You use your lungs when you breathe.
Key Points. 1  Lung cancer happens when cells in the lung change (mutate). They grow uncontrollably and cluster together to form a tumor. 2  Lung cells most often change because they are exposed to dangerous chemicals that we breathe. 3  There are two main types of lung cancer, small cell lung cancer and non-small cell lung cancer.