ABSTRACT
Cancer is a multifactorial disease with etiological agents being chemical, physical and biologic carcinogens. Oncogenes and tumor suppressor genes together maintain homeostasis in the cell. They control activities such as normal cellular growth, cellular differentiation and apoptosis. Any imbalance in homeostasis of these cells will lead to hyperplasia and reduced apoptosis. Further genetic abnormalities will lead to loss of DNA repair mechanism that causes uncontrolled proliferation of mutated cell leading to cancer. To understand the biology of cancer at cellular level, understanding of the normal cell cycle is mandatory and this chapter explains a detailed cell cycle. Tumor markers are biochemical or biological substances that are produced by tumors cells and secreted into blood, urine, other body fluids or body tissues higher in patients with certain types of cancer. A tumor marker may be produced by the tumor itself or by host body in response to the cancerous cells or in certain noncancerous conditions.
