Epidemiology of cancer

State and regional cancer registries are organizations that abstract clinical data about cancer from patient medical records. These institutions provide information to state and national public health groups to help track trends in cancer diagnosis and treatment. One of the largest and most important cancer registries is Surveillance Epidemiology and End Results (SEER), administered by the US Federal government.[5]

Health information privacy concerns have led to the restricted use of cancer registry data in the United States Department of Veterans Affairs[6][7][8] and other institutions.[9] The American Cancer Society predicts that approximately 1,690,000 new cancer cases will be diagnosed and 577,000 Americans will ultimately die of cancer in 2012.[10]

Observational epidemiological studies that show associations between risk factors and specific cancers mostly serve to generate hypotheses about potential interventions that could reduce cancer incidence or morbidity. Randomized controlled trials then test whether hypotheses generated by epidemiological studies and laboratory research actually result in reduced cancer incidence and mortality. In many cases, findings from observational epidemiological studies are not confirmed by randomized controlled trials.

The approximate relative levels of the preventable causes of cancer in the United States, taken from the article Cancer prevention.

The most significant risk factor is age. According to cancer researcher Robert A. Weinberg, "If we lived long enough, sooner or later we all would get cancer."[11] Essentially all of the increase in cancer rates between prehistoric times and people who died in England between 1901 and 1905 is due to increased lifespans.[11]

Although the age-related increase in cancer risk is well-documented, the age-related patterns of cancer are complex. Some types of cancer, like testicular cancer, have early-life incidence peaks, for reasons unknown. Besides, the rate of age-related increase in cancer incidence varies between cancer types with, for instance, prostate cancer incidence accelerating much faster than brain cancer.[12] It has been proposed that the age distribution of cancer incidence can be viewed as the distribution of probability to accumulate the required number of driver events by the given age.[13][14]

Over a third of cancer deaths worldwide (and about 75-80% of cancers in the United States[15]) are due to potentially modifiable risk factors. The leading modifiable risk factors worldwide are:

• tobacco smoking, which is strongly associated with lung cancer, mouth, and throat cancer;
• drinking alcohol, which is associated with a small increase in oral, esophageal, breast, liver and other cancers;
• a diet low in fruit and vegetables,
• physical inactivity, which is associated with increased risk of colon, breast, and possibly other cancers
• obesity, which is associated with colon, breast, endometrial, and possibly other cancers
• sexual transmission of human papillomavirus, which causes cervical cancer and some forms of anal cancer, vaginal cancer, vulvar cancer, penile cancer, rectal cancer, and oropharyngeal cancer.

Men with cancer are twice as likely as women to have a modifiable risk factor for their disease.[16]

Other lifestyle and environmental factors known to affect cancer risk (either beneficially or detrimentally) include the use of exogenous hormones (e.g., hormone replacement therapy causes breast cancer), exposure to ionizing radiation and ultraviolet radiation, and certain occupational and chemical exposures. A Western diet is associated with increased exposure of the gastrointestinal tract to bile acids that are produced by the body to digest fatty foods. Bile acids are likely endogenous etiologic agents in gastrointestinal cancer.[17]

Every year, at least 200,000 people die worldwide from cancer related to their workplace.[18] Millions of workers run the risk of developing cancers such as pleural and peritoneal mesothelioma from inhaling asbestos fibers, or leukemia from exposure to benzene at their workplaces.[18] Currently, most cancer deaths caused by occupational risk factors occur in the developed world.[18] It is estimated that approximately 20,000 cancer deaths and 40,000 new cases of cancer each year in the U.S. are attributable to occupation.[19]

New cancer diagnosis in the England in 2012

In the U.S. cancer is second only to cardiovascular disease as the leading cause of death;[20] in the UK it is the leading cause of death.[21] In many developing countries cancer incidence (insofar as this can be measured) appears much lower, most likely because of the higher death rates due to infectious disease or injury. With the increased control over malaria and tuberculosis in some Third World countries, incidence of cancer is expected to rise; in the Eastern Mediterranean region, for example, cancer incidence is expected to increase by 100% to 180% in the next 15 years due to increases in life expectancy, an increasing proportion of elderly people, and the successful control of childhood disease.[22] This is termed the epidemiologic transition in epidemiological terminology.

Cancer epidemiology closely mirrors risk factor spread in various countries. Hepatocellular carcinoma (liver cancer) is rare in the West but is the main cancer in China and neighbouring countries, most likely due to the endemic presence of hepatitis B and aflatoxin in that population. Similarly, with tobacco smoking becoming more common in various Third World countries, lung cancer incidence has increased in a parallel fashion.

Childhood cancer and cancer in adolescents is rare (about 150 cases per million yearly in the US). Leukemia (usually acute lymphoblastic leukemia) is the most common cancer in children aged 1–14 in the U.S., followed by the central nervous system cancers, neuroblastoma, Wilms' tumor, and non-Hodgkin's lymphoma.[20] Statistics from the SEER program of the US NCI demonstrate that childhood cancers increased 19% between 1975 and 1990, mainly due to an increased incidence in acute leukemia. Since 1990, incidence rates have decreased.[30]

The age of peak incidence of cancer in children occurs during the first year of life, in infants. The average annual incidence in the United States, 1975–1995, was 233 per million infants.[30] Several estimates of incidence exist. According to SEER,[30] in the United States:

• Neuroblastoma comprised 28% of infant cancer cases and was the most common malignancy among these young children (65 per million infants).
• The leukemias as a group (41 per million infants) represented the next most common type of cancer, comprising 17% of all cases.
• Central nervous system malignancies comprised 13% of infant cancer, with an average annual incidence rate of nearly 30 per million infants.
• The average annual incidence rates for malignant germ cell and malignant soft tissue tumors were essentially the same at 15 per million infants. Each comprised about 6% of infant cancer.

Teratoma (a germ cell tumor) often is cited as the most common tumor in this age group, but most teratomas are surgically removed while still benign, hence not necessarily cancer. Prior to the widespread routine use of prenatal ultrasound examinations, the incidence of sacrococcygeal teratomas diagnosed at birth was 25 to 29 per million births.

Female and male infants have essentially the same overall cancer incidence rates, a notable difference compared to older children.

White infants have higher cancer rates than black infants. Leukemias accounted for a substantial proportion of this difference: the average annual rate for white infants (48.7 per million) was 66% higher than for black infants (29.4 per million).[30]

Relative survival for infants is very good for neuroblastoma, Wilms' tumor and retinoblastoma, and fairly good (80%) for leukemia, but not for most other types of cancer.

• List of countries by cancer rate
• Epidemiology of breast cancer
• Cancer cluster
• Cancer research
• Genetic epidemiology
• Incidentaloma, a symptom-free tumor that is found accidentally and whose treatment may be unimportant

• CANCERMondial — International Agency for Research on Cancer (IARC)
• Cancer Epidemiology Resources — CancerIndex
• Surveillance, Epidemiology and End Results — National Cancer Institute
• Cancer's global footprint — Pulitzer Center