Lung cancer is the mass of abnormal cells that develop due to the uncontrolled growth of cells in the lungs. It is the leading cause of cancer-related deaths in the United States, followed by breast cancer, colon cancer, and prostate cancer. The cancer cells grow to form tumors that interfere with the normal functioning of the lungs, which is to provide oxygen to the body through the blood.
In almost all cases, the cancer of the lung starts in the pinkish-gray and spongy walls of the airway of the lungs, known as bronchi or bronchioles or the air sacs known as alveoli.
The two main types of lung cancers are non-small cell lung cancer and small-cell lung cancer based on the type of cell in which cancer started.
People who smoke have the greatest risk of lung cancer, though lung cancer can also occur in people who have never smoked. The risk of lung cancer increases with the length of time and the number of cigarettes you’ve smoked. If you quit smoking, even after smoking for many years, you can significantly reduce your chances of developing lung cancer.
Non–small cell lung cancer:
Non–small cell lung cancer usually starts in glandular cells of the outer part of the lung. This type is known as adenocarcinoma. It is the most common kind.
Another type is squamous cell carcinoma of the lung. This type of cancer starts in the thin, flat cells known as squamous cells. These cells make the lining of the large airways, called bronchi which then branch off from the trachea (windpipe) into the lungs. Large cell carcinoma is also a type of non–small cell lung cancer, but it is less common. There are several other rare types of non–small cell lung cancer including sarcomas and sarcomatoid carcinomas.
Small cell lung cancer: This type starts in cells that form the lining of the bronchi in the center of the lungs. There are different types of small cell lung cancer, including small cell carcinoma and combined small cell carcinoma (mixed type tumors of squamous or glandular cells).
There are other types of cancer that do not originate in the lung itself but are spread to the lungs, these are known as secondary lung cancer. Such kind of cancer starts in another part of the body and then spreads to the lungs (metastasis). These are not treated in the same way as primary lung cancer which starts in the lung only. Find out more about lung cancer treatment.
How does lung cancer develop?
Normally, the cells in the lungs or other parts of the body have a fixed growth and death cycle that regulates and maintains the number of cells in the body. In cancer, some cells develop a set of specific changes in their genetic makeup (DNA), known as mutations. When these mutations affect the genes of the cell, an uncontrolled and unregulated cell division occurs which changes the natural growth and death cycles of cells. This uncontrolled growth leads to the formation of a mass of abnormal cells, called a tumor.
Many studies have suggested that it takes a series of mutations to result in a lung cancer cell. Cells can be precancerous, before becoming fully cancerous, such that they may have some mutations but still function as normal lung cells.
In the case of lung cancer, the tumor or mass of abnormal cells are detected as nodules on a chest X-ray or CT scan. The tumor may be benign or malignant (cancerous).
The tumor cells are considered to be malignant when they are able to invade the normal tissues. When the malignant cells spread from the lung, the tumor is known to be lung cancer.