EPIDEMIOLOGY OF CANCER
The International Agency for Research on Cancer (IARC) estimates that over 14.1 million new incident cases of cancer (excluding non-melanoma skin cancer) occurred in 2012, of which over 8 million (57%) occurred in less developed regions (defined as Africa, Asia [excluding Japan], Latin America, and the Caribbean, plus Melanesia, Micronesia, and Polynesia in Oceania). Over 8.2 million deaths occurred, with over 5.3 million (65%) in less developed regions. This is predicted to increase to 21.7 million incident cases and 13 million deaths by 2030, with the majority of this increase being due to the aging of populations, as well as increased total population.
The 10 most common cancers diagnosed worldwide in 2012 were lung (13%), breast (12%), colon/rectum (10%), prostate (8%), stomach (7%), liver (6%), cervix (4%), oesophagus (3%), bladder (3%), and non-Hodgkin lymphoma (3%), with 8 of these being among the 10 most common causes of cancer death: lung (19%), stomach (9%), liver (9%), colon/rectum (9%), breast (6%), oesophagus (5%), prostate (4%), pancreas (4%), cervix (3%), and leukaemia (3%). These global estimates mask very large differences in regional incidence rates of specific cancers, with age-standardized incidence rates varying over five-fold between low- and high-incidence regions; for some cancers, there is a 20-fold difference between the lowest and highest incidence rates in individual countries. The burden of cancer on individual countries is a function of age-specific rates and population size. Thus, the country with the largest population in the world faces the largest number of cases of cancer, but the United States, with the world’s third largest population, has the second largest number of cases of cancer, owing to high age-specific rates, and a high proportion of people in older age groups.
In the United States, the most common cancers predicted for 2014 for men are prostate, (27%), lung (14%), colorectal (8%), bladder (7%), melanoma (5%), renal (5%), non-Hodgkin lymphoma (4%), oropharyngeal (4%), leukaemia (4%), and liver (3%), with 8 of these being among the 10 most common causes of cancer death: lung (28%), prostate (10%), colorectal (8%), pancreas (7%), liver (5%), leukaemia (5%), oesophagus (4%), bladder (4%), non-Hodgkin lymphoma (3%), and renal (3%), with the addition of pancreas (7%) and oesophagus (4%). For women, these are breast cancer (20%), lung (13%), colorectal (8%), uterine (6%), thyroid (6%), non-Hodgkin lymphoma (4%), melanoma (4%), renal (3%), pancreas (3%), and leukaemia (3%), with 7 of these being the among the top 10 causes of mortality: lung (26%), breast (15%), colon/rectum (9%), pancreas (7%), leukaemia (4%), uterine (3%), and non-Hodgkin lymphoma (3%), with the addition of ovary (5%), liver (3%), and brain and other nervous system (2%).
The rates of most cancers increase with age, often in a log-linear (exponential) fashion; any population that experiences increases in life expectancy in the proportion of the population in older age groups will almost inevitably see an increase in the numbers of cases of cancer. Some cancers have different age-incidence curves, notably cancers that occur mostly in the first few years of life, such as retinoblastoma and neuroblastoma, or in young adulthood, such as testicular cancer. Hodgkin lymphoma has a bimodal age incidence curve with peaks in younger and older adults. Breast cancer rates increase with age in premenopausal women but plateau or increase more slowly post-menopausally.
Male breast cancer occurs at less than 1% of the rate of female breast cancer in most countries. For cancers that occur in both sexes, age-specific rates are often two- to three-fold higher in men than women; for smoking-related cancers, this is often due to higher prevalence and duration of smoking among men.