Cancer is a disease at which some cells of an organism uncontrollable expand and extend to other parts of a body.

Cancer can begin practically in any place of the human body consisting of trillions of cells. Normal human cells grow and breed (through the process called by cell fission), forming the new cells necessary for an organism. When cells grow old or are damaged, they die, and their place is taken by new cells.

Sometimes this ordered process is broken, and the abnormal or damaged cells grow and breed when they do not. These cells can form tumors which represent fabric lumps. Tumors can be cancer or not cancer (good-quality).

Cancer tumors extend in nearby fabrics or interfere in them and also can move to the remote body parts, forming new tumors (this process is called innidiation). Cancer tumors can be also called malignant tumors. Many types of cancer form firm tumors, but the blood cancer, such as leukemia, usually does not form them.

Benign tumors do not extend in nearby fabrics and do not interfere in them. After removal benign tumors usually do not grow again while cancer tumors sometimes grow. However benign tumors can sometimes be quite big. Some of them can cause serious symptoms or to be life-threatening, for example, benign tumors in a brain.