Primary Lung Cancer and
Secondary Lung Cancer - Mesothelioma
Cancer is a disease related to the uncontrolled growth of tissue, leading to the formation of a mass (called a tumor or lesion.) Normal cells in the body divide and grow in an orderly, controlled manner. When cells grow uncontrollably and this growth invades other tissues or organs, the growths are said to be malignant, or cancerous. When a mass of tissue, or tumor, is benign, it is relatively stable and does not invade other tissues.
Cells from malignant tumors can break away and travel to other parts of the body, usually through the bloodstream, but also through the lymph system. When they find new host organs, these cells can grow into tumors in the new tissue. This spreading process is called metastasis, and when a cancer has reached an advanced stage in which the malignant cells are attacking other organs, it is said that the cancer tumors have metastasized. The tumors in new organs are always made up of cells similar to those of the original tumor.
Benign tumors do not metastasize. They can often be removed through surgery and not re-occur.
Lung cancer occurs when lung tissue develops cancerous growths. Primary lung cancer is cancer that originates in the lung tissue. Secondary lung cancer is cancer that spreads, or metastasizes, from other organs.
There are several different types of primary lung cancer. These are divided into two main groups:
- Small Cell Lung Cancer
- Non-small Cell Lung Cancer
Pleural mesothelioma is often thought of as a third type of primary lung cancer, but this is a misconception. Mesothelioma does not develop in the lungs, but rather in the serous membranes surrounding the lungs. As such, it does not fall into the typical categories of lung cancer. Mesothelioma can also occur in other tissues, including the lining of the abdomen (peritoneal mesothelioma) and in the lining of the heart (pericardial mesothelioma).
Small cell lung cancer comprises approximately 20 percent of the primary types of lung cancer. It is called small cell cancer because the tumor cells are very small, containing a nucleus and little more. Small cell cancer is also referred to as "oat cell" cancer. Chemotherapy is often suggested for this cancer in the early stages because of the rapid way in which it spreads. Surgery is not a good option to stop the spread early on. Small cell cancer is most closely linked to smoking; non-smokers rarely have it.
Non-small cell cancer falls into these categories:
- Squamous cell carcinoma
- Large cell carcinoma
- Adenosquamous cell carcinoma
- Undifferentiated carcinoma
The various categories of non-small cell cancer are physiologically similar to one another, and the way in which they respond to treatment is different from the way small cell lung cancer responds.
Squamous cell carcinoma is a common type of primary lung cancer. This type of cancer is also linked to smoking and it develops from the cells that line the airways in the lungs. Squamous cells are thin, flat cells that look like fish scales. Commonly the tumor growths are located in the center of the lungs near the large airways (bronchi). It is also referred to as epidermoid carcinoma. It comprises approximately 30 to 35 percent of the non-small cell cancer in the US, affecting men and the elderly most frequently.
Adenocarcinoma, like squamous cell carcinoma, develops from tissues in the lung airways. However, in contrast to squamous cell carcinoma, it develops from the glandular secretory tissues (tissues that produce mucus). It is often found in the outer airway passages, not the main bronchi, like the squamous cell variety. The incidence of this cancer is increasing. It comprises about 40 percent of non-small cell lung cancers in the U.S. and is the most common lung cancer among women.
Large cell lung cancer is named after its appearance. The cells look large and unnatural under the microscope. These types of cells grow quite quickly.
Adenosquamous carcinoma cells are cancer cells that appear flat under the microscope, like squamous cells, but derive from glandular secretory cells, like adenocarcinoma cells.
Undifferentiated carcinoma includes cancer cells that cannot be identified as one of the other groups. These cells appear abnormal in shape under the microscope and multiply uncontrollably.
Secondary lung cancer is cancer that has spread to the lungs from other organs. Many different types of cancer spread to the lungs, because of its significant blood supply. These include breast cancer and colon cancer.
The type of cancer is very important when it comes to treatment. The different types of cancer cells respond differently to different types of chemotherapy and other therapies. When cancer cells spread from other organs to the lungs, the lungs have to be treated for the other type of cancer, not lung cancer. This is an important distinction. For example, breast cancer that spreads to the lungs has to be treated for breast cancer, not lung cancer.
[Page updated September 2011]