Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these cells to invade other tissues, either by direct growth into adjacent tissue through invasion or by implantation into distant sites by metastasis. Metastasis is defined as the stage in which cancer cells are transported through the bloodstream or lymphatic system. Cancer may affect people at all ages, but risk tends to increase with age. It is one of the leading causes of death in developed countries.
There are many types of cancer. Severity of symptoms depends on the site and character of the malignancy and whether there is metastasis. A definitive diagnosis usually requires the histologic examination of tissue by a pathologist. This tissue is obtained by biopsy or surgery. Most cancers can be treated and some cured, depending on the specific type, location, and stage. Once diagnosed, cancer is usually treated with a combination of surgery, chemotherapy and radiotherapy. As research develops, treatments are becoming more specific for the type of cancer pathology. Drugs that target specific cancers already exist for several cancers. If untreated, cancers may eventually cause illness and death, though this is not always the case.
The unregulated growth that characterizes cancer is caused by damage to DNA, resulting in mutations to genes that encode for proteins controlling cell division. Many mutation events may be required to transform a normal cell into a malignant cell. These mutations can be caused by chemicals or physical agents called carcinogens, by close exposure to radioactive materials, or by certain viruses that can insert their DNA into the human genome. Mutations occur spontaneously, or are passed down generations as a result of germ line mutations.
More on [ Cancer ]

The accumulated evidence on lung cancer and environmental tobacco smoke - Paper in the British Medical Journal.
Environmental Tobacco Smoke - Cancer Facts from the National Cancer Institute. Summary and bibliography on effects of secondhand smoke. Additional publications you can send for.
Meta Description: [ Environmental Tobacco Smoke ]
Exposure to Spouse's Smoking Causes Lung Cancer - Long term smokers increase their spouses' risk of developing lung cancer by more than 20%, according to a new report.
Health Effects of Secondhand Smoke: Lung Cancer - Characterizes the risk and provides a bibliography of the research literature that establishes the risk.
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Involuntary Smoking - Summary of scientific evidence of exposure and cancer-causing effects of secondhand smoke.
Involuntary smoking causes breast cancer - Summary of Swiss study published in the American Journal of Epidemiology that studied 1300 women.
Meds.com: Environmental Tobacco Smoke - Focus is on lung cancer caused by secondhand smoke.
NERC Bibliography on Tobacco smoke and Cancer - Over 700 references to the scientific literature. From the National Environmental Respiratory Center.
OncoLink: Environmental Tobacco Smoke - Updated February 2000 to include latest research.
Meta Description: [ OncoLink staff physicians summarize journal articles both past and present which have impacted the standard of cancer care. ]
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Pets and Secondhand Smoke - Secondhand smoke causes diseases in cats and dogs.
Secondhand Smoke Causes Cancer - The largest review to date examined 50 studies on secondhand smoke, and concludes that secondhand smoke causes cancer of the lung, uterus, cervix, liver, and kidneys.
Meta Description: [ Exposure to second-hand tobacco smoke may increase the risk of developing a wide range of cancers by as much as 30%, say experts. ]
Secondhand Smoke Causes Cancer in Cats - According to recent research, secondhand smoke causes feline malignant lymphoma.
WHO: Passive Smoking Causes Lung Cancer - The World Health Organization (WHO) sets the record straight: secondhand smoke causes lung cancer in non-smokers.
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