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Tumor progression refers to the steps and stages a cancerous tumor passes through as it grows or spreads. The development of a single tumor generally includes three phases: hyperplasia, dysplasia, and carcinoma. Overall cancer progression with malignant tumors may also undergo four or more separate stages as the cancer metastasizes into other body areas.
Abnormal cell growth fuels a single tumor progression, and the alteration of a single cell lays the foundation for hyperplasia. The causes of the origin cell’s genetic alteration are often unknown. During hyperplasia, the cell keeps dividing uncontrollably, producing an overabundance of itself. These cells have reached the dysplasia phase when they begin to undergo structural changes that give them an unusual and irregular appearance. Once the cells cover a large contained area and succumb to functional changes that render them useless in their original duties, carcinoma has occurred.
A carcinoma in situ represents a single tumor. Tumors often appear as hard, compact masses because of the cells’ disorganized nature. They can occur in nearly any cell in the body, and thus tumors may be found on any organ. Cancers that occur in the blood or on the skin may take on a different or not clearly visible abnormal appearance. Any malignant tumor can begin the process of metastasis.
Metastasis facilitates tumor progression into other, previously unafflicted areas of the body. Mutations in two types of genes usually create conditions for tumor progression: oncogenes and tumor suppressors. Oncogenes are the substances in the body responsible for cellular division and cellular movement. Sometimes, a change in these genes can cause them to overexert influence, subsequently causing both rapid cell growth and a high concentration of protein. At the same time, mutations may inactivate tumor suppressor genes. These genes are the security guards that put a stop to abnormal cell division; if they are neutralized then the oncogenes perform their destructive behaviors unchecked.
Cancer progression is often divided into stages that characterize the initial tumor promotion or progression and the degree of metastasis. In addition to the aforementioned cellular makeup of the cells and the manifestation of spreading, other factors that determine a cancer's stage include tumor size, tumor location, and the particular role of lymph nodes in the cancer. Different staging systems are used, but one well-known system divides cancer and tumor progression into four stages. The more advanced stage three or stage four cancers generally include larger tumors and tumor cells that have reached the lymph nodes. In the most serious late-stage cancers, metastasis to surrounding organs has also occurred.
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