All forms of cancer begin in cells, the basic structural and functional units of all organisms. Cancers such as mesothelioma that arise from organs and solid tissues, are referred to as solid tumors; cancers that arise from blood cells are known as leukemias, multiple myelomas or lymphomas.
Under normal conditions, cells grow and divide to form new cells as they are needed by the body, but when this processes goes awry, new cells form when they are not needed. These additional cells form a mass of tissue, known as a tumor. Tumors are classified as “benign” (non-cancerous), or “malignant” (cancerous). Benign tumors do not spread to other parts of the body, and therefore, are rarely life-threatening, but malignant tumors have the potential to spread or metastasize, and may threaten life.
Cancer can begin in any organ or tissue of the body, and is usually named for the part of the body in which it starts. In the case of mesothelioma, it begins in the linings of either the lung, the abdominal cavity or, in rare cases, the heart, hence the terms pleural mesothelioma, peritoneal mesothelioma and pericardial mesothelioma. These original tumors are known as “primary tumors”.
Metastasis refers to spread of the cancer, and occurs when cancer cells break away from the primary tumor and enter the bloodstream or the lymphatic system where they are carried to other parts of the body. When a new tumor forms at a site away from the primary site, it is known as a “metastatic tumor”.
Cancer cells can spread anywhere in the body, but frequently spread to the lymph nodes near the primary tumor. This is called “lymph node involvement” or “regional disease”. Cancer that spreads to other organs or to lymph nodes far from the primary tumor site, is called “metastatic”, or “distant disease”.
To determine whether a tumor is primary or metastatic, pathologists examine a tissue sample of the tumor, and by using specialized diagnostic techniques, such as immunohistochemical chemical staining, are often able to determine where the cells originated. Metastatic cancer may be found at the same time as the primary tumor, or later, as a progression of the disease.
The goal of treatment for metastatic cancer may be either aggressive or palliative, depending on the type of primary cancer, the size and location of the metastasis, the patient’s age and overall health status and the types of treatment the patient has previously received. For patients who have failed first-line treatments with resulting metastatic disease, or who are diagnosed with late stage metastatic disease already present, clinical trials may be available.
Cancer metastasis remains a mystery to modern medicine. The process occurs when cancerous cells break away from a primary tumor and circulate to other parts of the body. Once they reach their new destination they initiate growth of new tumors.
Tumors can be of two types. Benign tumors only grow in one specific area of the body and do not spread to other areas. By contrast, malignant tumors can metastasize to other areas. The diagnosis as to the type of tumor is normally performed by a pathologist but benign tumors do risk becoming malignant and have to be closely monitored.
Metastasis is often found in the later stages of cancer. The more common places that a tumor will spread are the lungs, liver, brain, and bones. One of the mysteries of this process is that studies have shown over time that certain types of cancer often spread to specific parts of the body.
Malignant mesothelioma cells in the tumor break off and make their way to the extracellular matrix. This matrix is a layer of proteins that insulate a tumor from adjoining tissues. They send out cellular molecules that break them down allowing the malignant cells to escape.
Once they find a new location they begin to emit cellular signals to tissue which activate proteins that spur the growth of blood vessels (angiogenesis). The vessels are then able to compliment tumor growth by supplying nutrients and removing wastes.