Depending upon the type of cancer a patient has, they could exhibit various symptoms. The American Cancer Society has developed a general list of seven symptoms that could be warning signs of cancer :

• unusual bleeding or discharge (cancers of the ovaries or of the uterus)

• a lump that does not go away (cancer of the breast)

• a sore that does not heal within two weeks (cancers of the mouth)

• change in bowel or bladder habits (cancer of the colon or rectum)

• persistent hoarseness or cough (cancer of the lung)

• indigestion or difficulty swallowing (cancers of the esophagus or head and neck)

• change in a wart or mole (cancers of the skin)

Epidemiological studies are studies of cancer looking at various factors such as diet, race, age, and environment. These studies show that there are numerous factors that contribute to a patient being diagnosed with cancer. Two such factors are carcinogens and oncogenic viruses.

Carcinogens are substances known to cause and/or promote cancer. Carcinogens can be either man-made, such as cigarette smoke, or present naturally in the environment, as is ultraviolet radiation from the sun, both of which are known to play a major role in the development of cancer. Carcinogens can also enhance other factors that cause the cancer. Certain cancers develop slowly. It can take from 5 to 40 years for cancer to develop after exposure to a cancer-causing agent, making identification of carcinogens difficult. The number of exposures as well as the length of time exposed to carcinogens determine whether a cancer will develop, but there is no evidence that there is a "safe" level of any carcinogen. Some known carcinogens are:

• arsenic and some arsenic compounds (cancers of the lung)

• asbestos (cancers of the lung)

• benzene- a chemical used in the manufacture of plastics, paints, and adhesives also found in exhausts from cars and cigarette smoke (cancer of the bladder)

• anti-cancer drugs

• vinyl chloride

• tobacco (cancers of the lung, esophagus, and/or mouth)

• alcohol (cancers of the pancreas, head and neck, and/or liver)
  
  

These are pictures from the BRCA1 lab. Scientists work here studying the gene which is thought to cause breast cancer.

Oncogenes are genes within a cell that may initiate the cells' transformation from normal to malignant. Some known oncogenes are the BRCA 1 gene which is linked to breast cancer or the gene linked to colon cancer. Oncogenic viruses are viruses that are linked to cancer. There have been almost 40 oncogenic viruses discovered including HIV, HPV (Human Papilloma Viruses), herpes viruses, hepatitis B and C viruses, and retroviruses. Researchers have found that the immune system may recognize the difference between healthy cells and cancer cells and eliminate those that become cancerous. Cancer may develop when the immune system breaks down or is overwhelmed. This may account for the link between HIV and cancer.

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