This is how old, worn-out and damaged cells are replaced with healthy, new ones. Sometimes, a cell becomes abnormal and fails to do its job properly. When the cell divides, it makes more abnormal cells like itself. The abnormal cells divide even when the body does not need them. They form an abnormal mass of tissue, or a tumor.
Tumors can crowd out and destroy the healthy cells and tissues the body needs.
Tumors can be benign or malignant. Benign tumors are not cancer. They stay in one place and usually are not life-threatening. Benign tumors usually can be removed, and in most cases, they do not come back. Malignant tumors are cancer.