The epidemiology of cancer is the study of the factors affecting cancer, as a way to infer possible trends and causes. The study of cancer epidemiology uses epidemiological methods to find the cause of cancer and to identify and develop improved treatments.
This area of study must contend with problems of lead time bias and length time bias. Lead time bias is the concept that early diagnosis may artificially inflate the survival statistics of a cancer, without really improving the natural history of the disease. Length bias is the concept that slower growing, more indolent tumors are more likely to be diagnosed by screening tests, but improvements in diagnosing more cases of indolent cancer may not translate into better patient outcomes after the implementation of screening programs. A related concern is overdiagnosis, the tendency of screening tests to diagnose diseases that may not actually impact the patient's longevity. This problem especially applies to prostate cancer and PSA screening. [3]
Some cancer researchers have argued that negative cancer clinical trials lack sufficient statistical power to discover a benefit to treatment. This may be due to fewer patients enrolled in the study than originally planned. [4]
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.[ citation needed ]
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:[ citation needed ]
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.[ citation needed ] 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]
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, in 2008, cancer incidence was 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 an epidemiologic transition in epidemiological terminology.[ citation needed ]
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.[ citation needed ]
In 2015, more than 1,300 Indians died every day due to cancer. Between 2012 and 2014, the mortality rate due to cancer increased by approximately 6%. In 2012, there were 478,180 deaths out of 2,934,314 cases reported. In 2013 there were 465,169 deaths out of 3,016,628 cases. In 2014, 491,598 people died in out of 2,820,179 cases. [23] In 2013, the incidence and mortality of cancer is highest in the north-eastern region of India. [24] In 2015, breast cancer was the most common, and stomach cancer was the leading cause of death by cancer. In 2015, breast cancer and lung cancer killed the most women and men respectively. [25]
In 2007, cancer was the number one cause of death, contributing to 29.6% of all deaths in Canada. In 2007,the second highest cause of death was cardiovascular diseases, resulting in 21.5% of deaths. In 2011, prostate cancer was the most common form of cancer among males (about 28% of all new cases) and breast cancer the most common in females (also about 28% of all new cases).[ citation needed ]
The leading cause of death in both males and females is lung cancer, which contributes to 26.8% of all cancer deaths. Statistics indicate that between the ages of 20 and 50 years, the incidence rate of cancer is higher amongst women whereas after 50 years of age, the incidence rate increases in men. Predictions by the Canadian Cancer Society indicate that with time, there will be an increase in the rates of incidence of cancer for both males and females.[ citation needed ]
In 2008, cancer was responsible for 25% of all US deaths, with 30% of these from lung cancer. In 2008, the most commonly occurring cancer in men was prostate cancer, at about 25% of new cases. In 2008, amongst women, breast cancer was the most commonly occurring cancer, with about 25% of cancer diagnoses. Cancer can occur in children and adolescents, but it is uncommon, with about 150 cases per million in the U.S., with leukemia being the most common. [20] In the first year of life, the incidence is about 230 cases per million in the U.S., with the most common being neuroblastoma. [26] From 2004 to 2008, the US overall age-adjusted incidence of cancer was approximately 460 per 100,000 men and women per year. [27]
In 2008, cancer was responsible for about 25% of all US deaths. The statistics below are estimates for the U.S. in 2008, and may vary substantially in other countries. They exclude basal and squamous cell skin cancers, and carcinoma in situ in locations other than the urinary bladder. [20] As seen, breast/prostate cancer, lung cancer and colorectal cancer are responsible for approximately half of cancer incidence. The same applies for cancer mortality, but with lung cancer replacing breast/prostate cancer as the main cause.[ citation needed ]
In 2016, an estimated 1,685,210 new cases of cancer will be diagnosed in the United States and 595,690 people will die from the disease. [28]
Male | Female | |||
---|---|---|---|---|
Most common, by occurrence, 2008. [20] | Most common, by mortality, 2008. [20] | Most common, by occurrence, 2008. [20] | most common, by mortality, 2008. [20] | |
prostate cancer (25%) | lung cancer (31%) | breast cancer (26%) | lung cancer (26%) | |
lung cancer (15%) | prostate cancer (10%) | lung cancer (14%) | breast cancer (15%) | |
colorectal cancer (10%) | colorectal cancer (8%) | colorectal cancer (10%) | colorectal cancer (9%) | |
bladder cancer (7%) | pancreatic cancer (6%) | endometrial cancer (7%) | pancreatic cancer (6%) | |
non-Hodgkin lymphoma (5%) | liver & intrahepatic bile duct (4%) | non-Hodgkin lymphoma (4%) | ovarian cancer (6%) | |
skin melanoma (5%) | leukemia (4%) | thyroid cancer (4%) | non-Hodgkin lymphoma (3%) | |
kidney cancer (4%) | esophageal cancer (4%) | Skin melanoma (4%) | leukemia (3%) | |
oral and pharyngeal cancer (3%) | bladder cancer (3%) | ovarian cancer (3%) | uterine cancer (3%) | |
leukemia (3%) | non-Hodgkin lymphoma (3%) | kidney cancer (3%) | liver & intrahepatic bile duct (2%) | |
pancreatic cancer (3%) | kidney cancer (3%) | leukemia (3%) | brain and other nervous system (2%) | |
other (20%) | other (24%) | other (22%) | other (25%) |
In 2003, in the developed world, one in three people developed cancer during their lifetimes. If all cancer patients survived and cancer occurred randomly, the normal lifetime odds of developing a second primary cancer (not the first cancer spreading to a new site) would be one in nine. [29] However, cancer survivors have an increased risk of developing a second primary cancer, and the odds in 2003 were about one in 4.5. [29] About half of these second primaries can be attributed to the normal one-in-nine risk associated with random chance. [29]
The increased risk is believed to be primarily due to the same risk factors that produced the first cancer, such as the person's genetic profile, alcohol and tobacco use, obesity, and environmental exposures, and partly due, in some cases, to the treatment for the first cancer, which might have included mutagenic chemotherapeutic drugs or radiation. [29] Cancer survivors may be more likely to comply with recommended screening, and may be more likely than average to detect cancers. [29]
In 2008, childhood cancer and cancer in adolescents was rare, at about 150 cases per million yearly in the US. In 2008, leukemia, usually acute lymphoblastic leukemia, was 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] 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 in 1999:
Teratoma, a germ cell tumor, is often 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.[ citation needed ]
Female and male infants have essentially the same overall cancer incidence rates, a notable difference compared to older children.[ citation needed ]
In 1999, White infants had higher cancer rates than Black infants. Leukemias accounted for a substantial proportion of this difference. The average annual rate for white infants, at 48.7 per million, was 66% higher than for black infants, at 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.[ citation needed ]
General:
Lung cancer, also known as lung carcinoma, is a malignant tumor that begins in the lung. Lung cancer is caused by genetic damage to the DNA of cells in the airways, often caused by cigarette smoking or inhaling damaging chemicals. Damaged airway cells gain the ability to multiply unchecked, causing the growth of a tumor. Without treatment, tumors spread throughout the lung, damaging lung function. Eventually lung tumors metastasize, spreading to other parts of the body.
Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. It occurs when skin cells grow uncontrollably, forming malignant tumors. The primary cause of skin cancer is prolonged exposure to ultraviolet (UV) radiation from the sun or tanning devices. Skin cancer is the most commonly diagnosed form of cancer in humans. There are three main types of skin cancers: basal-cell skin cancer (BCC), squamous-cell skin cancer (SCC) and melanoma. The first two, along with a number of less common skin cancers, are known as nonmelanoma skin cancer (NMSC). Basal-cell cancer grows slowly and can damage the tissue around it but is unlikely to spread to distant areas or result in death. It often appears as a painless raised area of skin that may be shiny with small blood vessels running over it or may present as a raised area with an ulcer. Squamous-cell skin cancer is more likely to spread. It usually presents as a hard lump with a scaly top but may also form an ulcer. Melanomas are the most aggressive. Signs include a mole that has changed in size, shape, color, has irregular edges, has more than one color, is itchy or bleeds.
Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or a red or scaly patch of skin. In those with distant spread of the disease, there may be bone pain, swollen lymph nodes, shortness of breath, or yellow skin.
Prostate cancer is the uncontrolled growth of cells in the prostate, a gland in the male reproductive system below the bladder. Abnormal growth of prostate tissue is usually detected through screening tests, typically blood tests that check for prostate-specific antigen (PSA) levels. Those with high levels of PSA in their blood are at increased risk for developing prostate cancer. Diagnosis requires a biopsy of the prostate. If cancer is present, the pathologist assigns a Gleason score, and a higher score represents a more dangerous tumor. Medical imaging is performed to look for cancer that has spread outside the prostate. Based on the Gleason score, PSA levels, and imaging results, a cancer case is assigned a stage 1 to 4. A higher stage signifies a more advanced, more dangerous disease.
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bleeding, prolonged cough, unexplained weight loss, and a change in bowel movements. While these symptoms may indicate cancer, they can also have other causes. Over 100 types of cancers affect humans.
Uterine cancer, also known as womb cancer, includes two types of cancer that develop from the tissues of the uterus. Endometrial cancer forms from the lining of the uterus, and uterine sarcoma forms from the muscles or support tissue of the uterus. Endometrial cancer accounts for approximately 90% of all uterine cancers in the United States. Symptoms of endometrial cancer include changes in vaginal bleeding or pain in the pelvis. Symptoms of uterine sarcoma include unusual vaginal bleeding or a mass in the vagina.
Kidney cancer, also known as renal cancer, is a group of cancers that starts in the kidney. Symptoms may include blood in the urine, a lump in the abdomen, or back pain. Fever, weight loss, and tiredness may also occur. Complications can include spread to the lungs or brain.
Oral cancer, also known as oral cavity cancer, tongue cancer or mouth cancer, is a cancer of the lining of the lips, mouth, or upper throat. In the mouth, it most commonly starts as a painless red or white patch, that thickens, gets ulcerated and continues to grow. When on the lips, it commonly looks like a persistent crusting ulcer that does not heal, and slowly grows. Other symptoms may include difficult or painful swallowing, new lumps or bumps in the neck, a swelling in the mouth, or a feeling of numbness in the mouth or lips.
Malignancy is the tendency of a medical condition to become progressively worse; the term is most familiar as a characterization of cancer.
A case–control study is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute. Case–control studies are often used to identify factors that may contribute to a medical condition by comparing subjects who have the condition with patients who do not have the condition but are otherwise similar. They require fewer resources but provide less evidence for causal inference than a randomized controlled trial. A case–control study is often used to produce an odds ratio. Some statistical methods make it possible to use a case–control study to also estimate relative risk, risk differences, and other quantities.
In epidemiology, a risk factor or determinant is a variable associated with an increased risk of disease or infection.
Diseases of affluence, previously called diseases of rich people, is a term sometimes given to selected diseases and other health conditions which are commonly thought to be a result of increasing wealth in a society. Also referred to as the "Western disease" paradigm, these diseases are in contrast to "diseases of poverty", which largely result from and contribute to human impoverishment. These diseases of affluence have vastly increased in prevalence since the end of World War II.
Alcohol and cancer have a complex relationship. Alcohol causes cancers of the oesophagus, liver, breast, colon, oral cavity, rectum, pharynx, and larynx, and probably causes cancers of the pancreas. Cancer risk can occur even with light to moderate drinking. The more alcohol is consumed, the higher the cancer risk, and no amount can be considered completely safe.
Overdiagnosis is the diagnosis of disease that will never cause symptoms or death during a patient's ordinarily expected lifetime and thus presents no practical threat regardless of being pathologic. Overdiagnosis is a side effect of screening for early forms of disease. Although screening saves lives in some cases, in others it may turn people into patients unnecessarily and may lead to treatments that do no good and perhaps do harm. Given the tremendous variability that is normal in biology, it is inherent that the more one screens, the more incidental findings will generally be found. For a large percentage of them, the most appropriate medical response is to recognize them as something that does not require intervention; but determining which action a particular finding warrants can be very difficult, whether because the differential diagnosis is uncertain or because the risk ratio is uncertain.
Cancer is the leading cause of death in dogs. It is estimated that 1 in 3 domestic dogs will develop cancer, which is the same incidence of cancer among humans. Dogs can develop a variety of cancers and most are very similar to those found in humans. Dogs can develop carcinomas of epithelial cells and organs, sarcomas of connective tissues and bones, and lymphomas or leukemias of the circulatory system. Selective breeding of dogs has led certain pure-bred breeds to be at high-risk for specific kinds of cancer.
Male breast cancer (MBC) is a cancer in males that originates in their breasts. Males account for less than 1% of new breast cancers with about 20,000 new cases being diagnosed worldwide every year. Its incidence rates in males vs. females are, respectively, 0.4 and 66.7 per 100,000 person-years. The worldwide incidences of male as well as female breast cancers have been increasing over the last few decades. Currently, one of every 800 men are estimated to develop this cancer during their lifetimes.
Cancer survival rates vary by the type of cancer, stage at diagnosis, treatment given and many other factors, including country. In general survival rates are improving, although more so for some cancers than others. Survival rate can be measured in several ways, median life expectancy having advantages over others in terms of meaning for people involved, rather than as an epidemiological measure.
Worldwide, breast cancer is the most common invasive cancer in women. Breast cancer comprises 22.9% of invasive cancers in women and 16% of all female cancers.
Cancer is caused by genetic changes leading to uncontrolled cell growth and tumor formation. The basic cause of sporadic (non-familial) cancers is DNA damage and genomic instability. A minority of cancers are due to inherited genetic mutations. Most cancers are related to environmental, lifestyle, or behavioral exposures. Cancer is generally not contagious in humans, though it can be caused by oncoviruses and cancer bacteria. The term "environmental", as used by cancer researchers, refers to everything outside the body that interacts with humans. The environment is not limited to the biophysical environment, but also includes lifestyle and behavioral factors.
Childhood cancer is cancer in a child. About 80% of childhood cancer cases in high-income countries can be successfully treated via modern medical treatments and optimal patient care. However, only about 10% of children diagnosed with cancer reside in high-income countries where the necessary treatments and care is available. Childhood cancer represents only about 1% of all types of cancers diagnosed in children and adults, It is often more complex than adult cancers with unique biological characteristics and research and treatment is yet very challenging and limited. For this reason, childhood cancer is often ignored in control planning, contributing to the burden of missed opportunities for its diagnoses and management in countries that are low- and mid-income.