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Content: Lung cancer rates vary the most by state, reflecting historical differences in smoking prevalence that continue today. Who Is at Risk of Developing Cancer? Cancer usually develops in older people; 80% of all cancers in the United States are diagnosed in people 55 years of age or older. Certain behaviors also increase risk, such as smoking, having excess body weight, and drinking alcohol. In the US, approximately 39 out of 100 men and 38 out of 100 women will develop cancer during their lifetime (Table 6). These probabilities are estimated based on cancer occurrence in the general population and may overestimate or underestimate individual risk because of differences in exposures (e.g., smoking), family history, and/or genetic susceptibility. For most types of cancer, risk is higher with a family history of the disease. This is thought to result primarily from the inheritance of genetic variations that confer low or moderate risk and/or similar exposures to lifestyle/ environmental risk factors among family members, as opposed to inheritance of genetic alterations that confer a very high risk, which occurs much more rarely. Relative risk is the strength of the relationship between exposure to a given risk factor and cancer.