A malignant tumor is a tumor that is invasive, meaning it can invade the surrounding tissues. Malignant tumors contain cells that are cancerous, growing out of control and capable of metastasizing. Metastasize simply means that the cells of the tumor are able to leave the original tumor and travel to other parts of the body.

In cancerous tumors or malignant tumors, the cells have lost the ability to stop growing. In other words, they have gone rogue and will not stop dividing. To better explain, nearly every cell in the body is able to grow and divide to make new cells, to a certain extent. This is important for all living organisms. When cells go rogue, however, there is a problem with the DNA. When mutations, which are changes in the DNA sequence, occur, they cause the cells to forget how to stop dividing. After some time, the mass of cells becomes a tumor. The tumor can either be malignant or it can be benign, which means it is not cancerous.

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