What Is Cancer?

Cancer is the name given to a large group of diseases characterized by the uncontrolled growth and spread of abnormal cells. It may seem hard to understand how normal, healthy cells become cancerous, but if you think of a cell as a small computer, programmed to operate in a particular fashion, the process will become clearer.

Under normal conditions, healthy cells are protected by a powerful overseer, the immune system, as they perform their daily functions of growing, replicating, and repairing body organs. When something interrupts normal cell programming, however, uncontrolled growth and abnormal cellular development results in a new growth of tissue serving no physiologic function called a neoplasm. This neoplasmic mass often forms a clumping of cells known as a tumor.

Not all tumors are malignant (cancerous); in fact, most are benign (noncancerous). Benign tumors are generally harmless unless they grow in such a fashion as to obstruct or crowd out normal tissues or organs. A benign tumor of the brain, for instance, is life-threatening when it grows in a manner that causes blood restriction and results in a stroke. The only way to determine whether a given tumor or mass is benign or malignant is through biopsy, or microscopic examination of cell development.

Benign and malignant tumors differ in several key ways. Benign tumors are generally composed of ordinary-looking cells enclosed in a fibrous shell or capsule that prevents their spreading to other body areas. Malignant tumors are usually not enclosed in a protective capsule and can therefore spread to other organs. This process, known as metastasis, makes some forms of cancer particularly aggressive in their ability to overcome bodily defenses. By the time they are diagnosed, malignant tumors have frequently metastasized throughout the body, making treatment extremely difficult. Unlike benign tumors, which merely expand to take over a given space,
malignant cells invade surrounding tissue, emitting claw like protrusions that disrupt chemical processes within healthy cells. More specifically, malignant cells disturb the ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) within the normal cells. Tampering with these substances, which control cellular metabolism and reproduction, produces mutant cells that differ in form, quality, and function from normal cells.