In this section you can learn more about the known causes of cancer, Learn how potential carcinogens are tested and classified, find lists of known and. Find out the basics about cancer, including symptoms, causes and treatments. Learn steps you can take to prevent cancer. We don't know exactly what causes many cancers. But there are things that can increase your risk of getting cancer. Find out what to look out for and the.
of Cancer Causes Potential
Additionally, UV radiation, from exposure to the sun or tanning beds, is a powerful initiator in humans and is a cause of skin cancer. For this reason, long-term tamoxifen treatment is losing popularity in favor of aromatase inhibitors. These include exposure to radiation or the synthetic estrogen diethylstilbestrol DES.
Aflatoxin is produced by Aspergillus flavus and Aspergillus parasiticus fungi. The fungi synthesize aflatoxin when they are living in warm, moist conditions. These fungi are prevalent among crops such as rice, corn, cassava, nuts, peanuts, chilies, and spices. Countries with the highest amounts of these organisms lie within 40 degrees latitude north or south of the equator. Storage of food under warm, moist conditions increases the risk of aflatoxin contamination.
Aflatoxicosis is the disease that results from ingestion of aflatoxin. This disease can present in one of two forms. The first is an acute illness that results from exposure to large amounts of the toxin over a short period of time. Adult humans have a high tolerance for aflatoxin. Ingestion of large amounts of aflatoxin usually causes liver damage and acute illness but is rarely fatal.
However, exposure to high levels of the toxin can cause death in children. The second form of aflatoxicosis is due to low level chronic exposure to aflatoxin. Chronic aflatoxin exposure has an additive effect and can lead to the development of liver cancer. Aflatoxin increases the risk of liver cancer usually in the form of hepatocellular carcinoma or HCC in all persons who ingest contaminated food. It can also increase the risk of lung cancer in workers who handle the grain.
Infection with either the Hepatitis B or C viruses combined with exposure to aflatoxin can increase a person's risk of developing liver cancer by as much as 30 fold over a person who is exposed to aflatoxin but is not infected with hepatitis virus.
Infection with the Hepatitis B virus decreases a person's ability to detoxify aflatoxin via the liver. This can partially account for the greatly increased risk of cancer development in individuals exposed to both aflatoxin and hepatitis virus. In its initial stages, HCC causes no noticable symptoms. It can grow for up to 3 years before causing physical symptoms.
Non surgical treatments are only minimally effective. Liver transplantation is the only current cure for HCC. Unfortunately, based on the number, size, location, and severity of the underlying disease, not all patients are candidates for a transplant. Although most cancer seems to arise from environmental exposures to chemicals and radiation or lifestyle choices, a large number of cases are caused by infections.
As more is learned about different types of cancer, additional links with infectious agents are likely to be found. Parasites One of the first connections between infections and cancer was provided by Dr. Fibiger noticed an association between cancer in his laboratory rats and infection with a parasitic worm nematode.
He named the worm Spiroptera carcinoma. While it was later shown that the worms were not the primary cause of the cancer, the link between infection and cancer has withstood the test of time. Several different kinds of worm-like parasites trematodes are known to cause cancer.
The parasites are usually very small and have complicated life cycles, living in several different hosts at different stages in their lives. The life cycle of Clonorchis sinensis is shown above. Bacteria Helicobacter pylori pictured below is a bacteria that is able to survive in the mucosa of the gastric stomach epithelium for a long time and is a main cause of stomach and duodenal diseases. Epidemiological studies have provided evidence that H.
Viruses Some viruses have also been associated with the initiation and promotion of tumor growth based on both epidemiological and experimental evidence. Some DNA viruses contain genes whose products can take control of cell division in the host cell.
They promote the development of tumors by increasing proliferation rates and shutting down the normal systems that prevent cells from dividing. These viruses include human papillomavirus HPV , the most significant risk factor for the development of cervical cancer. This virus also protects infected cells from death apoptosis.
Some viruses also have indirect effects on tumor development. Hepatitis B causes damage that leads to increased cell division and inflammation in the liver, potentially promoting the growth of tumors. HIV infection may also make patients susceptible to infection by a type of human herpes virus, HHV 8, that is a risk factor for Kaposi's sarcoma Learn more about viruses that cause cancer.
Since , there has been a slight increase in obesity in women, and the rates in men and children have remained about the same. Even in the face of large amounts of research, new drugs, and community programs to fight weight gain 30 , America collectively struggles to slim down. Solid cancers associated with obesity include: Risk is also increased for blood cell cancers, including myeloma, leukemia, and non-Hodgkin's lymphoma But what does excess fat adipose tissue have to do with the abnormal cell behaviors seen in cancer?
It may help to think of fat deposits as another hormone -producing gland in the endocrine system 33 which includes the pineal gland, pancreas, ovaries, testes, hypothalamus, and adrenal glands. Some of these adipokines can have negative effects on the rest of your body in terms of cancer development and progression 31 34 32 Obesity is also associated with increased aromatase activity. Aromatase is an enzyme that produces estrogen from its building blocks androgens.
This leads to the production of too much estrogen. Estrogen can bind to cancer cells that have the estrogen receptor, and cause them to divide Aromatase expression is also induced by prostaglandin E2 PGE2 , another inflammatory molecule elevated in obesity. PGE2 is secreted by tumor cells, macrophages, and fat cells adipocytes When PGE2 binds to cells, it activates pathways that promote tumor growth, such as those for cell division, invasion, angiogenesis, and immunosuppression PGE2 production is controlled by the enzyme cyclooxygenase-2 COX-2 , which is shown to be found at higher amounts in patients with obesity-associated breast inflammation Insulin resistance in particular seems to be important in elevating cancer risk.
When we eat, the digestive system mouth, stomach and intestines breaks down the meal to free up sugars in the food. The energy-packed sugars are then absorbed into the bloodstream, where they can deliver energy to the body.
In response to rising blood-sugar levels, the pancreas produces insulin, which is a protein that attaches to cells and causes them to take in sugar from the bloodstream. The pancreas tries to compensate by churning out too much insulin.
The actions of insulin and related proteins, including its receptors and insulin-like growth factor -1 IGF-1 , have been associated with increased tumor growth, particularly for colon, breast, and prostate cancer The receptors for insulin can be upregulated in certain cancer cells 50 When insulin binds to receptors on cancer cells, it can activate cell proliferation pathways 51 and alter the metabolism of the cells by enhancing glucose transport — the end result is that more energy is made available to the cancer cells Insulin also increases the activity of IGF IGF-1 is a protein produced by the liver in response to growth hormone GH.
Insulin, however, can attach itself to these binding proteins, which frees up IGF-1 to do its dirty work. High IGF-1 levels have been correlated with prostate cancer, melanoma, colon cancer, and breast cancer When IGF-1 binds to its receptors, it can turn on genes that control cell reproduction and cell survival A study carried out in mice and published in March suggests that obesity-induced adipocyte degeneration could lead to chronic inflammation and insulin resistance When the fat cells die, their DNA is released into the surrounding tissue environment.
These results were supported by studies with human blood plasma samples. The microbiome is the collective genes found in the hundreds of species of bacteria living inside a person. Microbiome changes have been identified as another link between obesity and cancer. The bacteria living inside the gut are usually helpful; they break down and ferment foods and hard-to-digest fibers 54 , and they produce important nutrients such as biotin, vitamin K, and vitamin B12 Lean and obese individuals have different mixtures of bacteria in their guts.
Slimmer, healthier individuals tend to have lots of different kinds of bacteria, while obese individuals have less diversity Low bacterial diversity has also been associated with insulin resistance, abnormal blood lipid content dyslipidemia , and inflammation The bacterial community seems to specialize itself depending on the diet being consumed Why does this matter?
Obesity and a high-fat diet are associated with gut permeability and increases in the blood levels of bacterial lipopolysaccharides LPS. LPS is found in the membranes of some bacteria, including E.
This chronic inflammation can fuel tumorigenesis LPS in the blood have also been linked to weight gain, hyperglycemia, and insulin resistance A recent study in mice still to be validated in humans suggests another mechanism by which the microbiome can lead to obesity and insulin resistance.
Mice fed a high-fat diet had increased blood levels of acetate, which was later shown to be produced by their intestinal bacteria. This acetate would stimulate the parasympathetic nervous system, which would signal to beta-cells in the pancreas via the vagus nerve to secrete more insulin. The combination of a hearty appetite because of too much ghrelin and increased energy storage because of too much insulin is a recipe for obesity and insulin resistance To make matters worse, the types of bacteria seen in obese individuals has also been shown to be better at extracting energy or calories from food, and this can lead to further weight gain, metabolic dysregulation, and altered adipokine function Not only does obesity increase the likelihood of developing cancer, but it can also decrease the effectiveness of some cancer treatments, including chemotherapy, targeted therapy, and anti-angiogenic therapy Bevacizumab, an anti-angiogenesis drug that prevents tumors from growing a blood supply, is used in combination with conventional chemotherapy to extend colorectal patient survival.
A study published in the journal Gut suggests that visceral fat the fat stored around the internal organs in the abdominal cavity could be used to predict response to this bevacizumab-based therapy; more visceral fat means more tumor progression The researchers think that the extra VEGF the molecule that bevacizumab inhibits secreted by visceral fat decreases the effectiveness of the bevacizumab.
Another retrospective study found that obese women with breast cancer developed earlier metastases and had less successful response to first-line chemo treatment with paclitaxel than non-obese women Other researchers found that Chinese breast cancer patients with a higher BMI were less likely to achieve pathological complete response defined as the absence invasive carcinoma in breast tissue and lymph nodes of in biopsy after paclitaxel and carboplatin treatment than patients with a lower BMI Researchers found that in mouse models of pancreatic ductal carcinoma, obesity impaired the delivery and efficacy of chemotherapy drugs by decreasing vascular perfusion Vascular perfusion refers to the extent of blood vessels within a tissue and the resulting delivery of nutrients or drugs through the bloodstream.
They found that more adipocytes meant more pro-inflammatory cytokines and infiltration by tumor-associated neutrophils.
This obesity-associated inflammation was coupled with desmoplasia, the growth of dense, fibrous tissue. Desmoplasia makes it easier for cancer cells to spread 65 and more difficult for blood vessels to grow properly; thus, obesity-induced desmoplasia makes it more difficult for cancer drugs to affect a tumor.
In fact, of current research interest is the benefit of metformin for cancer patients Metformin is an anti-diabetic drug that improves insulin sensitivity, but it has also been shown to improve treatment outcomes and survival in diabetic cancer patients. In addition, metformin has been shown to reduce metastasis in animal models of pancreatic cancer.
Metformin may help by inhibiting the production of inflammatory molecules and by reducing desmoplasia The large-scale clinical trials needed to determine drug dosages for obese patients have not been conducted, and there is little information available to help clinicians understand the drug dynamics of anticancer agents in obese patients This could lead to an increased likelihood of remission and mortality This calculation can lead to some extraordinarily high-sounding doses of chemo for larger patients.
ASCO recommends that physicians should view obese and normal-weight patients equally in terms of chemotherapy dosages with exceptions for the maximums set on the use of carboplatin, bleomycin, and vincristine Read a feature story about the connection between obesity and cancer.
Chronic inflammation has been seen, both experimentally and epidemiologically, to be an important factor in tumor development. Chronic inflammation can be caused by viral or bacterial infections, autoimmune diseases and inflammatory conditions of unknown origins. It has been shown that mutation of key inflammatory control genes is associated with a higher risk of cancer progression, and markers of inflammation correlate with a worse prognosis for cancer patients.
Immune cells also produce oxygen radicals that can cause mutations in DNA. Inflammation can both induce carcinogenesis and lead to progression and metastasis. The activation of a specific transcription factor,NF-kB, by pro-inflammatory cytokines has been shown to produce a more aggressive cancer phenotype including resistance to normal growth control mechanisms, angiogenetic capability and metastasis.
Tumor associated macrophages TAM , are also associated with the inflammatory pathway, have been observed to produce pro-angiogenic factors and recruit blood vessels early in tumor development. TAM also increase the growth rate of tumor cells and cause the dissolution of the connective tissue matrix surrounding the tumor, enabling tumor growth and spread.
There are several cancer types associated with chronic inflammatory conditions, including; colon cancer and inflammatory bowel disease, liver cancer and hepatitis C, bladder or colon cancer and schistosomiasis a chronic parasitic infection and stomach cancer and H.
Bacteria have proven to be good models for determining the mutagenic potential of compounds. Bruce Ames, a biochemist, developed an assay to identify potential mutagens. The Ames test works 'backwards' from what one might expect. The test starts with mutant bacteria and looks for chemicals that can change them back into normal wild type bacteria.
In the Ames test, a potential mutagen is placed on a paper disc in the center of a petri dish on which only bacterial cells that mutate are able to grow. The mutagenic potential of the compound in question is determined by the amount of bacterial growth seen.
Information obtained in this way was shown to be comparable to results from tests in rodents. Researchers have also manipulated mouse cells to make them potential targets for carcinogens and have transferred genes from cancerous cells into healthy mice,--all of which have led to the conclusion that mutations in key genes can lead to the changes that result in cancer.
X-Radiation and Gamma Radiation. Soot, Coal Chimney Sweeping. B-cell Lymphoma , Nasal, Pharyngeal, Stomach. Hepatitis B and C. Tobacco is an herbaceous plant belonging to the Solanaceae family. The primary source of commercial tobacco is cultivated and harvested Nicotiana tabacum 76 Tobacco leaves contain nicotine, the chemical responsible for tobacco's addictive effects. To get these effects, the leaves can be chewed, smoked, or sniffed.
Nicotine's effects on the body include decreased appetite, elevated mood and feeling of well-being, increased heart rate and blood pressure, and stimulated memory and alertness. These effects don't last long and may be replaced by symptoms of nicotine withdrawal within hours after the last tobacco use. Symptoms of nicotine withdrawal include intense nicotine cravings, anxiety, depression, restlessness, headaches, increased appetite, and concentration problems The intensity of nicotine's effects as well as nicotine withdrawal symptoms depends on the level of nicotine present in the body.
In in the U. The Y-1 breed of tobacco was reported to have had the highest known nicotine yield in tobacco at that time, at 6. Y-1 tobacco was used in five brands of American cigarettes, but its usage was discontinued when the Food and Drug Administration FDA became concerned with nicotine-level manipulation Overview Smoking tobacco refers to tobacco that is heated and smoked.
Some common examples of smoking tobacco include cigarettes, cigars, and hookahs. It is important to note that while e-cigarettes do not contain tobacco and are not burned during use, their rise in popularity as "smoking" devices has led the FDA to propose that e-cigarettes be regulated as tobacco products 85 A section on e-cigarettes is included below. Cigarettes Each cigarette typically contains less than 1 gram of tobacco. Cigarettes are made of hundreds of chemicals that react in the presence of heat to produce thousands of chemicals.
Many of the chemicals that have been identified as cancer-causing agents carcinogens can be found in the sticky, partially burned residue known as "tar". Some of the remaining thousands of chemicals have been identified as toxic substances that may damage a person's health Some examples of the chemicals found in tobacco smoke are arsenic also found in rat poison , butane also found in lighter fluid , cadmium also found in battery acid , carbon monoxide also found in car exhaust fumes , nicotine also used as insecticide , and toluene also found in paints Smoking tobacco produces several powerful cancer-causing chemicals, including nitrosamines and benzo a pyrene.
Cigars Each cigar can contain between grams of tobacco, depending on the size of the cigar. Cigar smoke contains higher levels of toxins and carcinogens than cigarette smoke due to the type of tobacco and wrapping used.
This can lead to cancer. If a parent has these genes, they may pass on the altered instructions to their offspring. Some genetic changes occur after birth, and factors such as smoking and sun exposure can increase the risk. Other changes that can result in cancer take place in the chemical signals that determine how the body deploys, or "expresses" specific genes.
Finally, a person can inherit a predisposition for a type of cancer. A doctor may refer to this as having a hereditary cancer syndrome.
Inherited genetic mutations significantly contribute to the development of 5—10 percent of cancer cases. Doctors usually prescribe treatments based on the type of cancer, its stage at diagnosis, and the person's overall health.
The most common type of cancer in the U. Each year, more than 40, people in the country receive a diagnosis of one of the following types of cancer:.
Other forms are less common. According to the National Cancer Institute, there are over types of cancer. For example, sarcomas develop in bones or soft tissues, while carcinomas form in cells that cover internal or external surfaces in the body. Basal cell carcinomas develop in the skin, while adenocarcinomas can form in the breast.
Improvements in cancer detection, increased awareness of the risks of smoking, and a drop in tobacco use have all contributed to a year-on-year decrease in the number of cancer diagnoses and deaths. According to the American Cancer Society, the overall cancer death rate declined by 26 percent between and When a person has cancer, the outlook will depend on whether the disease has spread and on its type, severity, and location.
Cancer causes cells to divide uncontrollably. It also prevents them from dying at the natural point in their life cycle. Genetic factors and lifestyle choices, such as smoking, can contribute to the development of the disease.
Several elements affect the ways that DNA communicates with cells and directs their division and death. After nonmelanoma skin cancer, breast cancer is the most common type in the U. However, lung cancer is the leading cause of cancer-related death. Treatments are constantly improving. Examples of current methods include chemotherapy, radiation therapy, and surgery. Some people benefit from newer options, such as stem cell transplantation and precision medicine. Some cancers cause early symptoms, but others do not exhibit symptoms until they are more advanced.
Many of these symptoms are often from causes unrelated to cancer. The best way to identify cancer early is to report any unusual, persistent symptoms to your doctor so they can advise you on any further testing that may be needed.
Some symptoms of cancer can be found here. Article last reviewed by Mon 12 November All references are available in the References tab. The genetics of cancer. MNT is the registered trade mark of Healthline Media. Any medical information published on this website is not intended as a substitute for informed medical advice and you should not take any action before consulting with a healthcare professional. Privacy Terms Ad policy Careers.
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Register for a free account Sign up for a free Medical News Today account to customize your medical and health news experiences. Register take the tour. Table of contents What is cancer? Causes Treatments Types Outlook Takeaway.
Cancer cells do not die at the natural point in a cell's life cycle. The side effects of chemotherapy include hair loss. However, advances in treatment are improving the outlook for people with cancer. Smoking increases the risk of many different types of cancer.
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Learn about what causes cancer and factors that can increase your risk. We also have cancer prevention tips and bust some common myths. information about inherited genetic mutations that can cause cancer.) between a potential risk factor and an increased risk of cancer, and. Cancer is a disease caused by genetic changes leading to uncontrolled cell growth and tumor "Chapter Hormones and the Etiology of Cancer". In Bast RC.