Cancer can develop in the lungs in two ways. If it first forms in the lungs rather than some other part of the body it is called primary lung cancer. If it has spread to the lungs from a primary cancer elsewhere in the body it is secondary lung cancer. Physicians will often refer to a development like this as “lung cancer, secondary to…” (Whatever the primary cancer may be).
Cancerous tumors grow into millions of cells, and when a case of cancer has developed a substantial tumor or tumors some of these cells may break away from the primary cancer and travel in the bloodstream or the lymphatic system to another part of the body. While secondary lung cancer can develop from any source, the most common types of cancer to migrate to the lungs are colon cancer, breast, bladder, stomach or kidney cancer, and melanoma.
Secondary Lung Cancer Symptoms
Tumors that are formed in secondary cancer cases are always comprised of the same cell type as the primary cancer. Sometimes a lung cancer diagnosis may precede discovery of the primary cancer because the first symptoms to occur are in the lungs. Secondary lung cancer symptoms are not dissimilar from the symptoms for primary lung cancer, and may include:
- A persistent cough
- Shortness of breath
- Coughing up blood-stained phlegm
- Pain or discomfort in the chest
There are rare occasions when a secondary lung cancer diagnosis is made and the primary cancer cannot be found. This situation is called an “unknown primary,” certainly a disquieting circumstance for the patient. A secondary lung cancer can be identified as such because of the nature of the cells found in the malignant tissue. There are many types of lung cancer, but each has a characteristic cell type. Cancer that appears in the lungs and is comprised of cells not associated with primary lung cancer is diagnosed as secondary.
Secondary Lung Cancer and Asbestos
Mesothelioma is the medical term for the most lethal form of asbestos-caused cancer. It develops in the mesothelium, which is a thin membrane or tissue that lines and protects several organs and areas in the body. The pleural mesothelium, or pleura, is two areas of tissue – one that lines the wall of the chest cavity and one that wraps around the outer surface of both lungs.
The most common type of asbestos cancer is pleural mesothelioma – cancer of the lining of the lungs. Technically this is not lung cancer, but it is caused by asbestos fibers lodged in the pleura that got there because they were inhaled and then worked their way through the lung wall to the layer of tissue outside the lungs. About seventy percent of all mesothelioma cases occur in the chest cavity in the form of pleural mesothelioma.
Malignant pleural mesothelioma will metastasize, just as any other form of cancer. One of the most common points of metastasis for pleural mesothelioma is the lung; malignant cells develop on the other side of the lung wall from the pleura. In fact, pleural mesothelioma is often called “asbestos lung cancer” because it develops on the outer lining of the lungs and because it is the most prominent form of asbestos cancer.
Sources:
- Schwartz et al, Medscape, http://emedicine.medscape.com/article/426820-overview
- National Cancer Institute, http://www.cancer.gov/cancertopics/factsheet/Sites-Types/unknownprimary
- Orphanet Journal of Rare Diseases, Moore et al, 2008, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2652430/
