If you sense this happening, the burden often falls on the person with cancer to reassure people that cancer is not contagious. Injuries such as bruises, cuts, or broken bones cannot cause cancer. This idea is popular because a person may suffer an injury, see a doctor, and, coincidentally, a tumor, which has been there for awhile, is discovered. A fall or an injury to the breast cannot cause breast cancer. An athlete with a bruise or swelling in the leg will not develop a bone tumor.
Cancer is a very complex disease, arising from a combination of many different factors.
If there were one single cause of cancer, such as an injury, the cure would have been discovered long ago. Even with lung cancer, however, there is no one simple cause because not all smokers will develop lung cancer, and some people who have never smoked may develop the disease. Cancer is caused by many factors, and there is no one single cause to explain it. Many people believe that cancer runs in families, and that if one family member has it, others are likely to develop the disease. In these situations, the risk may be increased by other factors, such as poor diet, smoking, hormonal influences, or occupational exposure.