ശരീരത്തില്‍ ഒരു കാന്‍സര്‍ കോശം പോലും വളരാതിരിക്കാന്‍/Dr Jolly Thomson

ശരീരത്തില്‍ ഒരു കാന്‍സര്‍ കോശം പോലും വളരാതിരിക്കാന്‍/Dr Jolly Thomson
What Causes Cancer?
There is no one single cause for cancer. Scientists believe that it is the interaction of many factors together that produces cancer. The factors involved may be genetic, environmental, or constitutional characteristics of the individual.
Diagnosis, treatment, and prognosis for childhood cancers are different than for adult cancers. The main differences are the survival rate and the cause of the cancer. The overall five-year survival rate for childhood cancer is about 80%, while in adult cancers the survival rate is 68%. This difference is thought to be because childhood cancer is more responsive to therapy and a child can tolerate more aggressive therapy.
Childhood cancers often occur or begin in the stem cells, which are simple cells capable of producing other types of specialized cells that the body needs. A sporadic (occurs by chance) cell change or mutation is usually what causes childhood cancer. In adults, the type of cell that becomes cancerous is usually an epithelial cell. Epithelial cells line the body cavity and cover the body surface. Cancer occurs from environmental exposures to these cells over time. Adult cancers are sometimes referred to as acquired for this reason.
Cancer Risk Factors
As mentioned, some cancers, particularly in adults, have been associated with repetitive exposures or risk factors. A risk factor is anything that may increase a person's chance of developing a disease. A risk factor does not necessarily cause the disease, but it may make the body less resistant to it. The following risk factors and mechanisms have been proposed as contributing to cancer:
Lifestyle factors. Smoking, a high-fat diet, and working with toxic chemicals are examples of lifestyle choices that may be risk factors for some adult cancers. Most children with cancer, however, are too young to have been exposed to these lifestyle factors for any extended time.
Family history, inheritance, and genetics may play an important role in some childhood cancers. It is possible for cancer of varying forms to be present more than once in a family. It is unknown in these circumstances if the disease is caused by a genetic mutation, exposure to chemicals near a family's residence, a combination of these factors, or simply coincidence.
Some genetic disorders. For example, Wiskott-Aldrich and Beckwith-Wiedemann syndrome are known to alter the immune system. The immune system is a complex system that functions to protect our bodies from infection and disease. The bone marrow produces cells that later mature and function as part of the immune system. One theory suggests that the cells in the bone marrow, the stem cells, become damaged or defective, so when they reproduce to make more cells, they make abnormal cells or cancer cells. The cause of the defect in the stem cells could be related to an inherited genetic defect or exposure to a virus or toxin.
Exposures to certain viruses. Epstein-Barr virus and HIV, the virus that causes AIDS, have been linked to an increased risk of developing certain childhood cancers, such as Hodgkin and non-Hodgkin lymphoma. Possibly, the virus alters a cell in some way. That cell then reproduces an altered cell and, eventually, these alterations become a cancer cell that reproduces more cancer cells.
Environmental exposures. Pesticides, fertilizers, and power lines have been researched for a direct link to childhood cancers. There has been evidence of cancer occurring among nonrelated children in certain neighborhoods and/or cities. Whether prenatal or infant exposure to these agents causes cancer, or whether it is a coincidence, is unknown.
Some forms of high-dose chemotherapy and radiation. In some cases, children who have been exposed to these agents may develop a second malignancy later in life. These strong anticancer agents can alter cells and/or the immune system. A second malignancy is a cancer that appears as a result from treatment of a different cancer.
Cancer Genes
How do genes affect cancer growth?
The discovery of certain types of genes that contribute to cancer has been an extremely important development for cancer research. Over 90% of cancers are observed to have some type of genetic alteration. Some of these alterations are inherited, while others are sporadic, which means they occur by chance or occur from environmental exposures (usually over many years).