In 2008 approximately 12.7 million cancers were diagnosed (excluding non-melanoma skin cancers and other non-invasive cancers) and 7.6 million people died of cancer worldwide.^[3] Cancers as a group account for approximately 13% of all deaths each year with the most common being: lung cancer (1.3 million deaths), stomach cancer(803,000 deaths), colorectal cancer (639,000 deaths), liver cancer (610,000 deaths), and breast cancer (519,000 deaths).^[101] This makes invasive cancer the leading cause of death in the developed world and the second leading cause of death in the developing world.^[3] Over half of cases occur in the developing world.^[3]

Global cancer rates have been increasing primarily due to an aging population and lifestyle changes in the developing world.^[3] The most significant risk factor for developing cancer is old age.^[102] Although it is possible for cancer to strike at any age, most people who are diagnosed with invasive cancer are over the age of 65.^[102]According to cancer researcher Robert A. Weinberg, "If we lived long enough, sooner or later we all would get cancer."^[103] Some of the association between aging and cancer is attributed to immunosenescence,^[104] errors accumulated in DNA over a lifetime, and age-related changes in the endocrine system.^[105]

Some slow-growing cancers are particularly common. Autopsy studies in Europe and Asia have shown that up to 36% of people have undiagnosed and apparently harmless thyroid cancer at the time of their deaths, and that 80% of men develop prostate cancer by age 80.^[106][107] As these cancers, often very small, did not cause the person's death, identifying them would have represented overdiagnosis rather than useful medical care.

The three most common childhood cancers are leukemia (34%), brain tumors (23%), and lymphomas (12%).^[108] Rates of childhood cancer have increased between 0.6% per year between 1975 to 2002 in the United States^[109] and by 1.1% per year between 1978 and 1997 in Europe.^[108]