Risk Factors for Bone Cancer & Bone Cancer: Risk Factors ( SOURCE[- INTERNATE CALECTION )

Risk Factors for Bone Cancer

A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. For example, exposing skin to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for cancers of the lung, mouth, larynx, bladder, kidney, and several other organs. But having a risk factor, or even several, does not mean that you will get the disease. Most people with bone cancers do not have any apparent risk factors.

Genetic disorders

A very small number of bone cancers (especially osteosarcomas) appear to be hereditary and are caused by defects (mutations) in certain genes. Retinoblastoma is a rare eye cancer in children that can be hereditary. The inherited form of retinoblastoma is caused by a mutation (abnormal copy) of the RB1 gene. Those with this mutation also have an increased risk of developing bone or soft tissue sarcomas. Also, if radiation therapy is used to treat the retinoblastoma, the risk of osteosarcoma in the bones around the eye is even higher.

Finally, there are families with several members who have developed osteosarcoma without inherited changes in any of the known genes. The gene defects that may cause cancers in these families haven’t been discovered yet.

Chondrosarcomas

Multiple exostoses (sometimes called multiple osteochondromas) syndrome is an inherited condition that causes many bumps on a person’s bones. These bumps are made mostly of cartilage. They can be painful and deform and/or fracture bones. This disorder is caused by a mutation in any one of the 3 genes EXT1, EXT2, or EXT3. Patients with this condition have an increased risk of chondrosarcoma.

An enchondroma is a benign cartilage tumor that grows into the bone. People who get many of these tumors have a condition called multiple enchondromatosis. They have an increased risk of developing chondrosarcomas.

Chordomas

Chordomas seem to run in some families. The genes responsible have not yet been found, but familial chordoma has been linked to changes on chromosome 7.

Patients with the inherited syndrome tuberous sclerosis, which can be caused by defects (mutations) in either of the genes TSC1 and TSC2, seem to have a high risk of chordomas during childhood.

Paget disease

Paget disease is a benign (non-cancerous) but pre-cancerous condition that affects one or more bones. It results in formation of abnormal bone tissue and occurs mostly in people older than 50. Affected bones are heavy, thick, and brittle. They are weaker than normal bones and more likely to fracture (break). Most of the time, Paget disease is not life threatening. Bone cancer (usually osteosarcoma) develops in about 1% of those with Paget disease, usually when many bones are affected.

Radiation

Bones that have been exposed to ionizing radiation may also have a higher risk of developing bone cancer. A typical x-ray of a bone is not dangerous, but exposure to large doses of radiation does pose a risk. For example, radiation therapy to treat cancer can cause a new cancer to develop in one of the bones in the treatment area. Being treated when you are younger and/or being treated with higher doses of radiation (usually over 60 Gy) increases your risk of developing bone cancer.

Exposure to radioactive materials such as radium and strontium can also cause bone cancer because these minerals build up in bones.

Non-ionizing radiation, like microwaves, electromagnetic fields from power lines, cellular phones, and household appliances, does not increase bone cancer risk.

Bone marrow transplantation

Osteosarcoma has been reported in a few patients who have undergone bone marrow (stem cell) transplantation.

Injuries

People have wondered if injury to a bone can cause cancer. This has never been proven. Many people with bone cancer remember having hurt that part of their bone. Most doctors believe that these injuries did not cause the cancer. Instead, the cancer caused people to remember the incident or that the injury drew their attention to that bone, making them notice a problem that had already been present for some time.

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The American Cancer Society medical and editorial content team

Bone Cancer: Risk Factors

Approved by the Cancer.Net Editorial Board, 05/2017

ON THIS PAGE: You will find out more about the factors that increase the chance of developing this type of cancer. Use the menu to see other pages.

A risk factor is anything that increases a person’s chance of developing cancer. Although risk factors can often influence the development of cancer, most do not directly cause cancer. Some people with several risk factors never develop cancer, while others with no known risk factors do. Knowing your risk factors and talking about them with your doctor may help you make more informed lifestyle and health care choices.

The following factors may raise a person’s risk of developing bone cancer:

·        Genetics. Children with familial retinoblastoma, which is a type of eye cancer, have an increased risk of developing osteosarcoma. People with a history of sarcomas in their family, as is seen with Li-Fraumeni syndrome, are also at high risk for osteosarcomas. Researchers are finding genes that are passed from generation to generation that give people a higher risk of developing osteosarcoma than the general population. All of these conditions are rare.

·        Previous radiation therapy. People who have had radiation treatment for other conditions have a higher risk of developing bone cancer at the site of the radiation therapy. The majority of radiation therapy-caused sarcomas include angiosarcoma and UPS of soft tissue or osteosarcoma, but other types may occur.

·        Chemotherapy for another cancer. Some drugs, including alkylating agents and anthracyclines, used to treat cancer may increase the risk of developing a secondary cancer, usually osteosarcoma.

·        Benign tumors or other bone conditions. Paget’s disease of the bone may lead to osteosarcoma. Other noncancerous bone diseases, such as fibrous dysplasia, may increase the risk of osteosarcoma.

Prevention

Different factors cause different types of cancer. Researchers continue to look into what factors cause this type of cancer. Currently, there is no known way to prevent bone cancer. Early detection offers the best hope for successful treatment, so people with known risk factors are encouraged to visit the doctor regularly and discuss their personal risk for developing bone cancer. This includes people with Li-Fraumeni syndrome, retinoblastoma, or other conditions in which sarcomas are inherited. Still, most bone cancer occurs in people with no known risk factors.

The next section in this guide is Symptoms and Signs. It explains what body changes or medical problems this disease can cause. You may use the menu to choose a different section to read in this guide.    

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TYPES OF CANCER

Risks and causes

Find out about the risk factors of bone cancer.

We don’t know what causes most bone cancers. But there are some factors that may increase your risk of developing it.

Having any of these risk factors does not mean that you will definitely develop cancer.

Risks and causes

 Age

 Cancer treatments

 Other bone diseases

 Genetic factors

 Childhood cancer

Injuries and knocks

People often think that a knock or injury to a bone can cause a cancer. But research studies do not support this.

It's more likely that an injury causes swelling, which when it's investigated, shows up a cancer that is already there. Or a bone affected by cancer may be weakened and so is more likely to become damaged in an accident. Doctors may then spot the tumour when they are investigating your accident.

Other possible causes

Stories about potential causes are often in the media and it isn’t always clear which ideas are supported by evidence. There might be things you have heard of that we haven’t included here. This is because either there is no evidence about them or it is less clear.

What's to know about bone cancer?

Last updated Mon 11 December 2017

By Christian Nordqvist

Reviewed by Christina Chun, MPH

1.              Treatment

2.              Stages

3.              Causes

4.              Symptoms

5.              Types

6.              Diagnosis

7.              Outlook

Bone cancer describes a malignant tumor of the bone that destroys healthy bone tissue.

Bone cancer is divided into primary and secondary bone cancer: primary bone cancer forms in the cells of the bone and secondary bone cancer starts elsewhere, eventually spreading to bones.

In this article, we will discuss the survival rates, types, causes, symptoms, and treatments for bone cancer.

Fast facts on bone cancer:

·   Benign bone tumors are more common than malignant bone tumors.

·   There are a number of different bone cancer types.

·   Early symptoms might include pain in the affected area.

·   A range of diagnostic tests can help diagnose bone cancer.

·    Radiotherapy, chemotherapy, and surgery can all be used to treat bone cancer.

Treatment

The type of treatment for bone cancer depends on several factors, including:

·        the type of bone cancer

·        where it is located

·        how aggressive it is

·        whether it is localized or has spread

There are three approaches to treating bone cancer. These are surgery, radiation therapy, and chemotherapy.

Surgery

Surgery aims to remove the tumor and some of the bone tissue that surrounds it. If some of the cancer is left behind, it may continue to grow and eventually spread.

Limb-sparing surgery, also known as limb salvage surgery, means that surgical intervention occurs without having to amputate the limb. The surgeon may take some bone from another part of the body to replace lost bone, or an artificial bone may be fitted.

In some cases, however, amputation of a limb may be necessary.

Radiation therapy

Radiotherapy, machine pictured here, is commonly used for treating bone cancer and other forms of cancer.

Radiotherapy is commonly used in the treatment of many cancer types. It involves the use of high-energy X-rays or particles to destroy cancer cells. Radiotherapy works by damaging the DNA inside the tumor cells, preventing them from reproducing.

Radiotherapy can be used to:

·        cure the patient by completely destroying the tumor.

·        relieve pain in more advanced cancers.

·        shrink the tumor, making it easier to then surgically remove it.

·        eliminate the cancer cells that remained behind after surgery.

Combination therapy is radiotherapy combined with another type of therapy. This may be more effective in some cases.

Chemoradiation, or radiotherapy combined with chemotherapy, may also be used.

Chemotherapy

Chemotherapy involves the use of chemicals to treat disease. More specifically, it refers to the destruction of cancer cells. Chemotherapy has five possible goals:

·        Total remission: Chemotherapy aims to cure the patient. In some cases, chemotherapy alone can get rid of the cancer completely.

·        Combination therapy: Chemotherapy can help other therapies, such as radiotherapy or surgery, produce better results.

·        Delay or prevent recurrence: Chemotherapy, when used to prevent the return of cancer, is most often used after a tumor has been removed surgically.

·        Slow down cancer progression: Chemotherapy can slow down the advancement of the cancer.

Chemotherapy may also help to relieve symptoms; this is more frequently used for patients with advanced cancer.

Stages

Bone cancer is staged dependent on how advanced it is:

·        Stage 1: The cancer has not spread from the bone. The cancer is not aggressive.

·        Stage 2: This is the same as stage 1 but more aggressive.

·        Stage 3: Tumors exist in at least two places in the same bone.

·        Stage 4: The cancer has spread to other parts of the body.

The stage of the cancer will dictate how it is treated and the likelihood of survival.

Causes

While doctors are unsure or precise causes, patients with long-term inflammatory diseases, such as Paget's disease are at a significantly higher risk of developing bone cancer later in life. However, nobody can explain why one person gets bone cancer while another one does not. It is not contagious.

The following groups of people may be at a higher risk of developing bone cancer:

·        children or young adults aged up to 20 years

·        people who have received radiation therapy

·        individuals with a history of Paget's disease

·        people with a close relative who has bone cancer

·        individuals with hereditary retinoblastoma, a type of eye cancer that most commonly affects very young children

·        people with Li-Fraumeni syndrome, a rare genetic condition

Symptoms

The patient initially experiences pain in the affected area. Over time, the pain gets worse and continuous. In some cases, the pain is subtle, and the patient may not see a doctor for several months.

The progression of pain with Ewing sarcoma tends to be faster than in most other bone cancers. Typically, bone cancer pain is deep, nagging, and has a permanent character. Other symptoms include:

·        swelling in the affected area

·        weakened bones that resulting in a significantly higher risk of fracture

·        unintentional weight loss

·        a lump in the affected area

Although much less common, the patient might also experience fever, chills, and night sweats.

Types

There are many types of bone cancer, pictured here is myeloma of the bone marrow.

There are several types of bone cancer, including:

Primary bone cancers

Primary bone cancers are either benign tumors or cancers. Benign tumors can be due to developmental changes, trauma, infections, inflammation, or abnormal tissue growth; they are more common in people under the age of 30.

Examples of benign bone tumors include:

·        osteoma

·        osteoid osteoma

·        osteochondroma

·        osteoblastoma

·        enchondroma

·        giant cell tumor of the bone

·        aneurysmal bone cyst

·        fibrous dysplasia of the bone

Examples of malignant primary bone tumors include:

·        osteosarcoma

·        chondrosarcoma

·        Ewing's sarcoma

·        malignant fibrous histiocytoma

·        fibrosarcoma

·        other sarcomas

Multiple myeloma is a blood cancer that may include one or more bone tumors. Certain bone cancers are found in specific bones; for instance, teratomas and germ cell tumors are frequently located in the tailbone.

Osteosarcoma

Osteosarcoma is the most common type of bone cancer. It usually develops in children and young adults. After leukemia and brain tumors, osteosarcoma is the third most common cancer among teens in the United States.

Ewing sarcoma

Ewing sarcoma usually develops in the pelvis, shinbone, or thighbone. It most commonly affects teenagers and young adults.

Chondrosarcoma

Chondrosarcoma usually develops in adults. It starts in the cartilage cells and moves on to the bone.

Diagnosis

A doctor may order a blood test to rule out other possible causes. The patient will then be referred to a bone specialist. The following diagnostic tests may be ordered:

·        bone scan

·        CT scan

·        MRI scan

·        positron emission tomography (PET)

·        X-rays

·        bone biopsy

Outlook

The outlook for a patient with malignant bone cancer depends mainly on whether it has spread to other parts of the body. If the cancer is localized (has not spread), the prognosis is usually good.

According to the University of Rochester Medical Centre, United Kingdom, for all bone cancers combined, the 5-year survival rate is around 70 percent.

The survival rate varies depending on the staging of the disease. The National Cancer Institute, U.S. estimates that by the end of 2016, there will have been 3,300 new cases and 1,490 deaths from cancer of the bones and joints.

Cancer Risk Factors

·        Cancer risk factor facts*

·        What are cancer risk factors?

·        Age and cancer risk

·        Alcohol

·        Cancer-causing substances in the environment

·        Chronic inflammation

·        Diet

·        Hormones

·        Immunosuppression

·        Infectious agents

·        Obesity

·        Radiation

·        Sunlight

·        Tobacco

·        CANCER RISK FACTORS CENTER

·        Cancer 101 Pictures Slideshow

·        Breast Cancer Slideshow

·        Skin Cancer Slideshow

·        Patient Comments: Cancer Risk Factors - Tobacco

·        Patient Comments: Cancer Risk Factors - Chemicals and Substances

·        Patient Comments: Cancer Risk Factors - Family History

·        Find a local Oncologist in your town

·        Cancer risk factor facts*

·        What are cancer risk factors?

·        Age and cancer risk

·        Alcohol

·        Cancer-causing substances in the environment

·        Chronic inflammation

·        Diet

·        Hormones

·        Immunosuppression

·        Infectious agents

·        Obesity

·        Radiation

·        Sunlight

·        Tobacco

Cancer Prevention

Most experts are convinced that many cancers can either be prevented or the risk of developing cancers can be markedly reduced. Some of the methods are simple; others are relatively extreme, depending on an individual's view.

Prevention of cancer, by avoiding its potential causes, is the simplest method. First on most clinicians and researchers list is to stop (or better, never start) smoking tobacco. Avoiding excess sunlight (by decreasing exposure or applying sunscreen) and many of the chemicals and toxins are excellent ways to avoid cancers. Avoiding contact with certain viruses and other pathogens also are likely to prevent some cancers. People who have to work close to cancer-causing agents (chemical workers, X-ray technicians, ionizing radiation researchers, asbestos workers) should follow all safety precautions and minimize any exposure to such compounds. Although the FDA and the CDC suggests that there is no scientific evidence that definitively says cell phones cause cancer, other agencies call for more research or indicate the risk is very low. Individuals who are concerned can limit exposure to cell phones by using an earpiece and simply make as few cell phone calls as possible.

Learn more about preventing cancer »

Cancer risk factor facts*

*Cancer risk factor facts by John P. Cunha, DO, FACOEP

• The most common risk factors for cancer include aging, tobacco, sun exposure, radiation exposure, chemicals and other substances, some viruses and bacteria, certain hormones, family history of cancer, alcohol, poor diet, lack of physical activity, or being overweight.
• Some causes of cancer can be prevented but others such as family history or aging cannot.
• You can help prevent many forms of cancer by quitting smoking, staying out of the sun and using sunscreen regularly, follow all safety precautions if you work with dangerous chemicals, do not have unprotected sex or share needles, get the vaccine that prevents hepatitis B infection if you are at risk for getting hepatitis B, drink in moderation, eat a balanced diet, exercise, and maintain a healthy weight.

It is usually not possible to know exactly why one person develops cancer and another doesn't. But research has shown that certain risk factors may increase a person's chances of developing cancer. (There are also factors that are linked to a lower risk of cancer. These are sometimes called protective risk factors, or just protective factors.)

Cancer risk factors include exposure to chemicals or other substances, as well as certain behaviors. They also include things people cannot control, like age and family history. A family history of certain cancers can be a sign of a possible inherited cancer syndrome.

Most cancer risk (and protective) factors are initially identified in epidemiology studies. In these studies, scientists look at large groups of people and compare those who develop cancer with those who don't. These studies may show that the people who develop cancer are more or less likely to behave in certain ways or to be exposed to certain substances than those who do not develop cancer.

Such studies, on their own, cannot prove that a behavior or substance causes cancer. For example, the finding could be a result of chance, or the true risk factor could be something other than the suspected risk factor. But findings of this type sometimes get attention in the media, and this can lead to wrong ideas about how cancer starts and spreads.

When many studies all point to a similar association between a potential risk factor and an increased risk of cancer, and when a possible mechanism exists that could explain how the risk factor could actually cause cancer, scientists can be more confident about the relationship between the two.

The list below includes the most-studied known or suspected risk factors for cancer. Although some of these risk factors can be avoided, others -- such as growing older -- cannot. Limiting your exposure to avoidable risk factors may lower your risk of developing certain cancers.

• Age
• Alcohol
• Cancer-Causing Substances
• Chronic Inflammation
• Diet
• Hormones
• Immunosuppression
• Infectious Agents
• Obesity
• Radiation
• Sunlight
• Tobacco

Age and cancer risk

Advancing age is the most important risk factor for cancer overall, and for many individual cancer types. According to the most recent statistical data from NCI's Surveillance, Epidemiology, and End Results program, the median age of a cancer diagnosis is 66 years. This means that half of cancer cases occur in people below this age and half in people above this age. One-quarter of new cancer cases are diagnosed in people aged 65 to 74.

A similar pattern is seen for many common cancer types. For example, the median age at diagnosis is 61 years for breast cancer, 68 years for colorectal cancer, 70 years for lung cancer, and 66 years for prostate cancer.

But the disease can occur at any age. For example, bone cancer is most frequently diagnosed among people under age 20, with more than one-fourth of cases occurring in this age group. And 10 percent of leukemias are diagnosed in children and adolescents under 20 years of age, whereas only 1 percent of cancer overall is diagnosed in that age group. Some types of cancer, such as neuroblastoma, are more common in children or adolescents than in adults.

Alcohol

Drinking alcohol can increase your risk of cancer of the mouth, throat, esophagus, larynx (voice box), liver, and breast. The more you drink, the higher your risk. The risk of cancer is much higher for those who drink alcohol and also use tobacco.

Doctors advise people who drink to do so in moderate amounts. The federal government's Dietary Guidelines for Americans defines moderate alcohol drinking as up to one drink per day for women and up to two drinks per day for men.

It has been suggested that certain substances in red wine, such as resveratrol, have anticancer properties. However, there is no evidence that drinking red wine reduces the risk of cancer.

Cancer-causing substances in the environment

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Cancer is caused by changes to certain genes that alter the way our cells function. Some of these genetic changes occur naturally when DNA is replicated during the process of cell division. But others are the result of environmental exposures that damage DNA. These exposures may include substances, such as the chemicals in tobacco smoke, or radiation, such as ultraviolet rays from the sun.

People can avoid some cancer-causing exposures, such as tobacco smoke and the sun's rays. But others are harder to avoid, especially if they are in the air we breathe, the water we drink, the food we eat, or the materials we use to do our jobs. Scientists are studying which exposures may cause or contribute to the development of cancer. Understanding which exposures are harmful, and where they are found, may help people to avoid them.

The substances listed below are among the most likely carcinogens to affect human health. Simply because a substance has been designated as a carcinogen, however, does not mean that the substance will necessarily cause cancer. Many factors influence whether a person exposed to a carcinogen will develop cancer, including the amount and duration of the exposure and the individual's genetic background.

• Aflatoxins
• Aristolochic Acids
• Arsenic
• Asbestos
• Benzene
• Benzidine
• Beryllium
• 1,3-Butadiene
• Cadmium
• Coal Tar and Coal-Tar Pitch
• Coke-Oven Emissions
• Crystalline Silica (respirable size)
• Erionite
• Ethylene Oxide
• Formaldehyde
• Hexavalent Chromium Compounds
• Indoor Emissions from the Household Combustion of Coal
• Mineral Oils: Untreated and Mildly Treated
• Nickel Compounds
• Radon
• Secondhand Tobacco Smoke (Environmental Tobacco Smoke)
• Soot
• Strong Inorganic Acid Mists Containing Sulfuric Acid
• Thorium
• Vinyl Chloride
• Wood Dust

Chronic inflammation

Inflammation is a normal physiological response that causes injured tissue to heal. An inflammatory process starts when chemicals are released by the damaged tissue. In response, white blood cells make substances that cause cells to divide and grow to rebuild tissue to help repair the injury. Once the wound is healed, the inflammatory process ends.

In chronic inflammation, the inflammatory process may begin even if there is no injury, and it does not end when it should. Why the inflammation continues is not always known. Chronic inflammation may be caused by infections that don't go away, abnormal immune reactions to normal tissues, or conditions such as obesity. Over time, chronic inflammation can cause DNA damage and lead to cancer. For example, people with chronic inflammatory bowel diseases, such as ulcerative colitis and Crohn disease, have an increased risk of colon cancer.

Many studies have investigated whether anti-inflammatory medications, such as aspirin or non-steroidal anti-inflammatory drugs, reduce the risk of cancer. However, a clear answer is not yet available.

Diet

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Many studies have looked at the possibility that specific dietary components or nutrients are associated with increases or decreases in cancer risk. Studies of cancer cells in the laboratory and of animal models have sometimes provided evidence that isolated compounds may be carcinogenic (or have anticancer activity).

But with few exceptions, studies of human populations have not yet shown definitively that any dietary component causes or protects against cancer. Sometimes the results of epidemiologic studies that compare the diets of people with and without cancer have indicated that people with and without cancer differ in their intake of a particular dietary component.

However, these results show only that the dietary component is associated with a change in cancer risk, not that the dietary component is responsible for, or causes, the change in risk. For example, study participants with and without cancer could differ in other ways besides their diet, and it is possible that some other difference accounts for the difference in cancer.

When evidence emerges from an epidemiologic study that a dietary component is associated with a reduced risk of cancer, a randomized trial may be done to test this possibility. Random assignment to dietary groups ensures that any differences between people who have high and low intakes of a nutrient are due to the nutrient itself rather than to other undetected differences. (For ethical reasons, randomized studies are not generally done when evidence emerges that a dietary component may be associated with an increased risk of cancer.)

Scientists have studied many additives, nutrients, and other dietary components for possible associations with cancer risk. These include:

• Acrylamide: Acrylamide is a chemical found in tobacco smoke and some foods. It can be produced when certain vegetables, such as potatoes, are heated to high temperatures. Studies in animal models have found that acrylamide exposure increases the risk for several types of cancer. However, there is no consistent evidence that dietary acrylamide exposure is associated with the risk of any type of cancer in humans.
• Alcohol: Although red wine has been suspected of reducing cancer risk, there is no scientific evidence for such an association. Also, alcohol is a known cause of cancer. Heavy or regular alcohol consumption increases the risk of developing cancers of the oral cavity (excluding the lips), pharynx (throat), larynx (voice box), esophagus, liver, breast, colon, and rectum. The risk of developing cancer increases with the amount of alcohol a person drinks.
• Antioxidants: Antioxidants are chemicals that block the activity of other chemicals, known as free radicals, that may damage cells. Laboratory and animal research has shown that exogenous antioxidants can help prevent the free radical damage associated with the development of cancer, but research in humans has not demonstrated convincingly that taking antioxidant supplements can help reduce the risk of developing or dying from cancer. Some studies have even shown an increased risk of some cancers.
• Artificial sweeteners: Studies have been conducted on the safety of several artificial sweeteners, including saccharin, aspartame, acesulfame potassium, sucralose, neotame, and cyclamate. There is no clear evidence that the artificial sweeteners available commercially in the United States are associated with cancer risk in humans.
• Calcium: Calcium is an essential dietary mineral that can be obtained from food and supplements. Research results overall support a relationship between higher intakes of calcium and reduced risks of colorectal cancer, but the results of studies have not always been consistent. Whether a relationship exists between higher calcium intakes and reduced risks of other cancers, such as breast and ovarian cancer, is unclear. Some research suggests that a high calcium intake may increase the risk of prostate cancer.
• Charred meat: Certain chemicals, called HCAs and PAHs, are formed when muscle meat, including beef, pork, fish, and poultry, is cooked using high-temperature methods. Exposure to high levels of HCAs and PAHs can cause cancer in animals; however, whether such exposure causes cancer in humans is unclear.
• Cruciferous vegetables: Cruciferous vegetables contain chemicals known as glucosinolates, which break down into several compounds that are being studied for possible anticancer effects. Some of these compounds have shown anticancer effects in cells and animals, but the results of studies with humans have been less clear.
• Fluoride: Fluoride in water helps to prevent and can even reverse tooth decay. Many studies, in both humans and animals, have shown no association between fluoridated water and cancer risk.
• Garlic: Some studies have suggested that garlic consumption may reduce the risk of developing several types of cancer, especially cancers of the gastrointestinal tract. However, the evidence is not definitive.
• Tea: Tea contains polyphenol compounds, particularly catechins, which are antioxidants. Results of epidemiologic studies examining the association between tea consumption and cancer risk have been inconclusive. Few clinical trials of tea consumption and cancer prevention have been conducted and their results have also been inconclusive.
• Vitamin D: Vitamin D helps the body use calcium and phosphorus to make strong bones and teeth. It is obtained primarily through exposure of the skin to sunlight, but it can also be obtained from some foods and dietary supplements. Epidemiologic studies in humans have suggested that higher intakes of vitamin D or higher levels of vitamin D in the blood may be associated with a reduced risk of colorectal cancer, but the results of randomized studies have been inconclusive.

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Hormones

Estrogens, a group of female sex hormones, are known human carcinogens. Although these hormones have essential physiological roles in both females and males, they have also been associated with an increased risk of certain cancers. For instance, taking combined menopausal hormone therapy (estrogen plus progestin, which is a synthetic version of the female hormone progesterone) can increase a woman's risk of breast cancer. Menopausal hormone therapy with estrogen alone increases the risk of endometrial cancer and is used only in women who have had a hysterectomy.

A woman who is thinking about menopausal hormone therapy should discuss the possible risks and benefits with her doctor.

Studies have also shown that a woman's risk of breast cancer is related to the estrogen and progesterone made by her ovaries (known as endogenous estrogen and progesterone). Being exposed for a long time and/or to high levels of these hormones has been linked to an increased risk of breast cancer. Increases in exposure can be caused by starting menstruation early, going through menopause late, being older at first pregnancy, and never having given birth. Conversely, having given birth is a protective factor for breast cancer.

Diethylstilbestrol (DES) is a form of estrogen that was given to some pregnant women in the United States between 1940 and 1971 to prevent miscarriages, premature labor, and related problems with pregnancy. Women who took DES during pregnancy have an increased risk of breast cancer. Their daughters have an increased risk of a cancer of the vagina or cervix. The possible effects on the sons and grandchildren of women who took DES during pregnancy are being studied.

Immunosuppression

Many people who receive organ transplants take medications to suppress the immune system so the body won't reject the organ. These "immunosuppressive" drugs make the immune system less able to detect and destroy cancer cells or fight off infections that cause cancer. Infection with HIV also weakens the immune system and increases the risk of certain cancers.

Research has shown that transplant recipients are at increased risk of a large number of different cancers. Some of these cancers can be caused by infectious agents, whereas others are not. The four most common cancers among transplant recipients and that occur more commonly in these individuals than in the general population are non-Hodgkin lymphoma (NHL) and cancers of the lung, kidney, and liver. NHL can be caused by Epstein-Barr virus (EBV) infection, and liver cancer by chronic infection with the hepatitis B (HBV) and hepatitis C (HCV) viruses. Lung and kidney cancers are not generally thought to be associated with infection.

People with HIV/AIDS also have increased risks of cancers that are caused by infectious agents, including EBV; human herpesvirus 8, or Kaposi sarcoma-associated virus; HBV and HCV, which cause liver cancer; and human papillomavirus, which causes cervical, anal, oropharyngeal, and other cancers. HIV infection is also associated with increased risks of cancers that are not thought to be caused by infectious agents, such as lung cancer.

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