Normally, body’s cells grow and divide to form new cells as body needs them. When cells grow old or become damaged, they die, and new cells take their place. But in case of cancer abnormal, old or damaged cells don’t die and new cells form when they are not needed. These extra cells can divide without stopping and may form growths called tumors. Many cancers form solid tumors, which are masses of tissue. Cancers of the blood, such as leukemias, generally do not form solid tumors.
Cancerous tumors can spread into or invade nearby tissues and are called malignant. As these tumors grow, some cancer cells break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor.
Unlike malignant tumors, benign tumors do not spread into, or invade, nearby tissues. Benign tumors, when removed, usually don’t grow back, whereas malignant tumors sometimes do.