What is Cancer?
WHAT IS CANCER AND HOW DOES IT FORM
Cancer is a constellation of diseases that is characterized by unrestrained cell growth; it may occur in any part of the body such as an organ, soft tissues, or the bone marrow, or blood factory. In health, normal cells grow and multiply in an orderly manner in a process referred to as cell division; when individual cells are damaged, they die in a process called apoptosis, programmed cell death, and are replaced by new cells.
Cancer disrupts the orderly process of cell growth and replacement; the uncontrolled cells multiply and form “tumors” or lumps of cells. Alternatively, tumors may
also form if the normal cell process of aging or apoptosis, is disrupted. Regardless of the mechanism of tumor growth, these lumps may be cancerous, malignant, or non-cancerous, benign.
Cancerous tumors may spread to other nearby tissues or organs and they have the ability to travel through the blood stream and lymphatic circulation to distant organs and tissues; this is called metastasis. Contrary to malignant cancer, benign tumors do not spread, however, benign tumors may grow large, cause serious symptoms and may be life-threatening. An example would be a benign tumor of the brain.
Many scientists today, believe that cancer is a genetic disease. In general cancer is caused by defects in genes that control cellular function, especially the function of cell growth and cell division. Broadly, speaking, there exist three major categories of cancer genes: ONCOGENES, TUMOR SUPPRESSOR GENES and DNA REPAIR GENES. The former promotes cancer cell growth, whereas the latter inhibits cancer cell growth.
Under normal circumstances there is a counterbalance between oncogenes and tumor suppressor genes. When the oncogene is altered in cells there is a stimulus for cells to divide and grow, cell suppression is overwhelmed and tumors form when they should not. When the tumor suppressor gene is dysfunctional or mutated, cells divide and grow without restraint, and programmed cell death does not occur and tumors form when they should not.
DNA repair genes are involved in fixing damaged DNA. Cells with mutations in these genes tend to develop additional mutations in other genes and changes in their chromosomes, such as duplications and deletions of chromosome parts. Certain environmental factors, such as ultraviolet light from sun exposure, tobacco smoke, radiation and certain chemicals such as hydrocarbons have been implicated in DNA injury. Together, these mutations may cause the cells to become cancerous.