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Metastasis is the process of spreading of a cancer that has been relatively inactive in a relatively fixed location throughout the body. Most likely this process appears because of the surgery which cuts into the cancer to cut the tumor out, but sometimes a small piece remains uncut and as far as the protective wall around the formerly inactive, or slow-growing cancer is disrupted, cancer cells can get into the blood and in that way they are carried to other parts of the body. The result is usually the appearance of the new growing cancer.
There are two main classifications of tumors: they can be either benign or malignant. Benign tumors cannot spread by metastasis while malignant tumors can. That's why only malignant tumors appears to be "cancer". Sometimes tumors with benign histology behave as malignant tumors, for example in brain tumors. The treatment of this kind of tumors must be as aggressive as of malignant disease. Patients diagnosed with cancer want to know whether their disease is local or has spread to other locations. This very ability to spread all over the body makes cancer such a life-threatening disease. That's why it is essential to understand why metastasis is possible at all.
Commonly metastasis can be found in the late stages of cancer. Metastases can spread with the help of the blood or the lymphatics or through both routes. The adrenals, liver, brain and the bones are the most common places for the metastases to occur. Some tumors have a propensity to seed in particular organs. This fact was called "seed and soil" theory by Stephen Paget a century ago in 1889. For example, bones are the preferable place of seed of prostate cancer and the liver - of colon cancer.
The cancer that appeared as a result of metastasis is called a secondary, or metastatic tumor. The cells of the secondary tumor are the same as in the original tumor. For instance, if breast cancer metastasizes to the lung, then the new tumor will consists of abnormal breast cells and not abnormal lung cells.
The next problem is the possibility of cancer cells to spread to lymph nodes near the primary tumor. This process was called regional disease or nodal involvement. Commonly the spread to regional lymph nodes that are situated near the primary tumor is not a marker of the development of the second tumor, but it is a sign of worse prognosis. Mesothelioma is a very aggressive type of cancer that can spread in other organs and tissues. Almost always it is incurable.
As it was determined earlier mesothelioma is by definition malignant. It is always a big problem to control its growth. Mesothelioma as any malignant kind of cancer has a tendency to spread the cancer all over the body.
Mesothelioma spreads around the body like all other types of malignant tumors by invading of surrounding tissues by the cancer cell. Often cancer cells can enter the blood stream or the lymphatics.
There are a lot of ways for mesothelioma to spread. For example pleural mesothelioma can metastasize the lungs, forming a secondary lung cancer whose cells would be similar to those of the primary cancer. It is possible to diagnose the cancer of the lung as a secondary cancer and this in its turn can help to identify the point-of-origin; pleural mesothelioma.
For the process of replication cancer cells requires essential nutrients and a continuous flow of oxygen. Secreting of the Vascular Endothelial Growth Factors (VEGF) induces blood vessel growth into the tumor to ease the process of oxygen and nutrients delivery.
Vascular Endothelial Growth Factors are a family of proteins that are used for stimulating of the survival and growth of the vascular system: arteries arterioles, capillaries and veins. One can usually find an overexpression of VEGF in most malignant mesothelioma cases.
The process described above is called angiogenesis. It is a natural process that is necessary for wound healing. But unfortunately it also plays a big role in metastasis of cancerous tumors. There are special angiogenesis inhibitors that halt production of VEGF. It helps to prevent the formation of new blood vessels. These inhibitors can be produced synthetically and can be used in treatment of the mesothelioma (anti-angiogenesis drugs).
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