The altered gene starts sending a wrong or garbled message, and the cell begins to multiply rapidly until it forms a lump known as a cancerous or malignant tumor. Neoplasms or tumors are classified as benign or malignant. Benign tumors are quite common, and they do not invade or destroy surrounding tissues. As such, they do not typically cause a health problem. Malignant tumors, on the other hand, are life threatening because they have the ability to invade tissues and destroy the host.
Tumors usually start to grow at a single site called the primary site.
In some instances, cancer cells have the capacity to metastasize, or spread, from the primary site to distant secondary sites. If cancer metastasizes, it is usually because small pieces of cancer cells break off from the original tumor and travel to other parts of the body. Metastasis is one of the primary reasons why cancer is a lethal disease and why it may occur through various routes. For instance, the tumor may form blood vessels, allowing cancer cells to enter the bloodstream through the tumor's capillaries. The cancer cells then implant onto the vessel walls of target organs throughout the body, where they continue to grow.