Cancer refers to any one of a large number of diseases characterized by the development of abnormal cells that divide uncontrollably and have the ability to infiltrate and destroy normal body tissue. Cancer often has the ability to spread throughout your body.
Cancer is the second-leading cause of death in the world. But survival rates are improving for many types of cancer, thanks to improvements in cancer screening, treatment and prevention.
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Signs and symptoms caused by cancer will vary depending on what part of the body is affected.
Some general signs and symptoms associated with, but not specific to, cancer, include:
- Lump or area of thickening that can be felt under the skin
- Weight changes, including unintended loss or gain
- Skin changes, such as yellowing, darkening or redness of the skin, sores that won't heal, or changes to existing moles
- Changes in bowel or bladder habits
- Persistent cough or trouble breathing
- Difficulty swallowing
- Persistent indigestion or discomfort after eating
- Persistent, unexplained muscle or joint pain
- Persistent, unexplained fevers or night sweats
- Unexplained bleeding or bruising
When to see a doctor
Make an appointment with your doctor if you have any persistent signs or symptoms that concern you.
If you don't have any signs or symptoms, but are worried about your risk of cancer, discuss your concerns with your doctor. Ask about which cancer screening tests and procedures are appropriate for you.
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Cancer is caused by changes (mutations) to the DNA within cells. The DNA inside a cell is packaged into a large number of individual genes, each of which contains a set of instructions telling the cell what functions to perform, as well as how to grow and divide. Errors in the instructions can cause the cell to stop its normal function and may allow a cell to become cancerous.
What do gene mutations do?
A gene mutation can instruct a healthy cell to:
- Allow rapid growth. A gene mutation can tell a cell to grow and divide more rapidly. This creates many new cells that all have that same mutation.
- Fail to stop uncontrolled cell growth. Normal cells know when to stop growing so that you have just the right number of each type of cell. Cancer cells lose the controls (tumor suppressor genes) that tell them when to stop growing. A mutation in a tumor suppressor gene allows cancer cells to continue growing and accumulating.
- Make mistakes when repairing DNA errors. DNA repair genes look for errors in a cell's DNA and make corrections. A mutation in a DNA repair gene may mean that other errors aren't corrected, leading cells to become cancerous.
These mutations are the most common ones found in cancer. But many other gene mutations can contribute to causing cancer.
What causes gene mutations?
Gene mutations can occur for several reasons, for instance:
- Gene mutations you're born with. You may be born with a genetic mutation that you inherited from your parents. This type of mutation accounts for a small percentage of cancers.
- Gene mutations that occur after birth. Most gene mutations occur after you're born and aren't inherited. A number of forces can cause gene mutations, such as smoking, radiation, viruses, cancer-causing chemicals (carcinogens), obesity, hormones, chronic inflammation and a lack of exercise.
Gene mutations occur frequently during normal cell growth. However, cells contain a mechanism that recognizes when a mistake occurs and repairs the mistake. Occasionally, a mistake is missed. This could cause a cell to become cancerous.
How do gene mutations interact with each other?
The gene mutations you're born with and those that you acquire throughout your life work together to cause cancer.
For instance, if you've inherited a genetic mutation that predisposes you to cancer, that doesn't mean you're certain to get cancer. Instead, you may need one or more other gene mutations to cause cancer. Your inherited gene mutation could make you more likely than other people to develop cancer when exposed to a certain cancer-causing substance.
It's not clear just how many mutations must accumulate for cancer to form. It's likely that this varies among cancer types.
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- Myths about cancer causes
While doctors have an idea of what may increase your risk of cancer, the majority of cancers occur in people who don't have any known risk factors. Factors known to increase your risk of cancer include:
Cancer can take decades to develop. That's why most people diagnosed with cancer are 65 or older. While it's more common in older adults, cancer isn't exclusively an adult disease — cancer can be diagnosed at any age.
Certain lifestyle choices are known to increase your risk of cancer. Smoking, drinking more than one drink a day for women and up to two drinks a day for men, excessive exposure to the sun or frequent blistering sunburns, being obese, and having unsafe sex can contribute to cancer.
You can change these habits to lower your risk of cancer — though some habits are easier to change than others.
Your family history
Only a small portion of cancers are due to an inherited condition. If cancer is common in your family, it's possible that mutations are being passed from one generation to the next. You might be a candidate for genetic testing to see whether you have inherited mutations that might increase your risk of certain cancers. Keep in mind that having an inherited genetic mutation doesn't necessarily mean you'll get cancer.
Your health conditions
Some chronic health conditions, such as ulcerative colitis, can markedly increase your risk of developing certain cancers. Talk to your doctor about your risk.
The environment around you may contain harmful chemicals that can increase your risk of cancer. Even if you don't smoke, you might inhale secondhand smoke if you go where people are smoking or if you live with someone who smokes. Chemicals in your home or workplace, such as asbestos and benzene, also are associated with an increased risk of cancer.
Cancer and its treatment can cause several complications, including:
- Pain. Pain can be caused by cancer or by cancer treatment, though not all cancer is painful. Medications and other approaches can effectively treat cancer-related pain.
- Fatigue. Fatigue in people with cancer has many causes, but it can often be managed. Fatigue associated with chemotherapy or radiation therapy treatments is common, but it's usually temporary.
- Difficulty breathing. Cancer or cancer treatment may cause a feeling of being short of breath. Treatments may bring relief.
- Nausea. Certain cancers and cancer treatments can cause nausea. Your doctor can sometimes predict if your treatment is likely to cause nausea. Medications and other treatments may help you prevent or decrease nausea.
- Diarrhea or constipation. Cancer and cancer treatment can affect your bowels and cause diarrhea or constipation.
- Weight loss. Cancer and cancer treatment may cause weight loss. Cancer steals food from normal cells and deprives them of nutrients. This is often not affected by how many calories or what kind of food is eaten; it's difficult to treat. In most cases, using artificial nutrition through tubes into the stomach or vein does not help change the weight loss.
- Chemical changes in your body. Cancer can upset the normal chemical balance in your body and increase your risk of serious complications. Signs and symptoms of chemical imbalances might include excessive thirst, frequent urination, constipation and confusion.
- Brain and nervous system problems. Cancer can press on nearby nerves and cause pain and loss of function of one part of your body. Cancer that involves the brain can cause headaches and stroke-like signs and symptoms, such as weakness on one side of your body.
- Unusual immune system reactions to cancer. In some cases the body's immune system may react to the presence of cancer by attacking healthy cells. Called paraneoplastic syndromes, these very rare reactions can lead to a variety of signs and symptoms, such as difficulty walking and seizures.
- Cancer that spreads. As cancer advances, it may spread (metastasize) to other parts of the body. Where cancer spreads depends on the type of cancer.
- Cancer that returns. Cancer survivors have a risk of cancer recurrence. Some cancers are more likely to recur than others. Ask your doctor about what you can do to reduce your risk of cancer recurrence. Your doctor may devise a follow-up care plan for you after treatment. This plan may include periodic scans and exams in the months and years after your treatment, to look for cancer recurrence.
Doctors have identified several ways to reduce your risk of cancer, such as:
- Stop smoking. If you smoke, quit. If you don't smoke, don't start. Smoking is linked to several types of cancer — not just lung cancer. Stopping now will reduce your risk of cancer in the future.
- Avoid excessive sun exposure. Harmful ultraviolet (UV) rays from the sun can increase your risk of skin cancer. Limit your sun exposure by staying in the shade, wearing protective clothing or applying sunscreen.
- Eat a healthy diet. Choose a diet rich in fruits and vegetables. Select whole grains and lean proteins. Limit your intake of processed meats.
- Exercise most days of the week. Regular exercise is linked to a lower risk of cancer. Aim for at least 30 minutes of exercise most days of the week. If you haven't been exercising regularly, start out slowly and work your way up to 30 minutes or longer.
- Maintain a healthy weight. Being overweight or obese may increase your risk of cancer. Work to achieve and maintain a healthy weight through a combination of a healthy diet and regular exercise.
- Drink alcohol in moderation, if you choose to drink. If you choose to drink alcohol, do so in moderation. For healthy adults, that means up to one drink a day for women and up to two drinks a day for men.
- Schedule cancer screening exams. Talk to your doctor about what types of cancer screening exams are best for you based on your risk factors.
- Ask your doctor about immunizations. Certain viruses increase your risk of cancer. Immunizations may help prevent those viruses, including hepatitis B, which increases the risk of liver cancer, and human papillomavirus (HPV), which increases the risk of cervical cancer and other cancers. Ask your doctor whether immunization against these viruses is appropriate for you.
By Mayo Clinic Staff
Dec. 07, 2022
Cancer is a disease caused when cells divide uncontrollably and spread into surrounding tissues. Cancer is caused by changes to DNA. Most cancer-causing DNA changes occur in sections of DNA called genes. These changes are also called genetic changes.What is the biggest cause of cancer? ›
Smoking and tobacco
If you smoke, stopping is the best thing you can do for your health and to reduce your cancer risk.
While plenty of research has shown that stress can cause cancer to grow and spread in mice, studies haven't shown a clear link between stress and cancer outcomes in people. But it's difficult to study stress in people for several reasons, including challenges with defining and measuring stress.Why do healthy people get cancer? ›
The main reasons are genetics and certain environmental or behavioral triggers. The tendency to develop some types of cancer is believed to be inherited — that is, the genes you were born with might carry a predisposition for cancer.What chemicals cause cancer? ›
Certain chemicals, including benzene, beryllium, asbestos, vinyl chloride and arsenic, are known human carcinogens, meaning they have been found to cause cancer in humans.What are the 3 known causes of cancer? ›
Smoking, a high-fat diet, and working with toxic chemicals are examples of lifestyle choices that may be risk factors for some adult cancers. Most children with cancer, however, are too young to have been exposed to these lifestyle factors for any extended time.What is the most killer cancer? ›
Lung and bronchus cancer is responsible for the most deaths with 130,180 people expected to die from this disease. That is nearly three times the 52,580 deaths due to colorectal cancer, which is the second most common cause of cancer death. Pancreatic cancer is the third deadliest cancer, causing 49,830 deaths.Does cancer show up in blood work? ›
Most blood tests aren't used on their own to diagnose cancer. But they can provide clues that may lead your health care team to make the diagnosis. For most types of cancer, a procedure to remove a sample of cells for testing is often needed to be sure.Does sugar cause cancer? ›
Sugar is not a carcinogenic (cancer-causing) substance. However, over-consumption of sugar, particularly added sugars in processed beverages and foods, can contribute to obesity which is an important risk factor for cancer. There is no evidence that consuming sugar makes cancer cells grow faster or cause cancer.Why are so many people getting cancer? ›
Risk factors such as highly processed foods, sugary beverages, obesity, Type 2 diabetes, sedentary lifestyle, and alcohol consumption have all significantly increased since the 1950s.
A new study shows sleeping less than six hours per night may increase your risk to develop a key sign of early colon cancer by about 50 percent. Patients who reported short sleep durations are far more likely to be diagnosed with colorectal adenomas, a precursor to cancer tumors.Is cancer caused by emotions? ›
Emotions affect both hormones and immune function. However, the link between mind-body interactions and cancer is far less clear and remains unproved. There is a vast difference between saying that stress temporarily alters some functions of the immune system and saying that stress, therefore causes cancer.Can depression cause cancer? ›
People with anxiety and depression sometimes manage stress poorly by engaging in unhealthy behavior. Some manage stress by drinking or smoking, while others overeat. Depression can cause fatigue, which often results in lack of exercise. All of these behaviors can result in health issues that can lead to cancer.Can you sense that you have cancer? ›
How does cancer cause signs and symptoms? A cancer can grow into,or begin to push on nearby organs, blood vessels, and nerves. This pressure causes some of the signs and symptoms of cancer. A cancer may also cause symptoms like fever, extreme tiredness (fatigue), or weight loss.How long can you have cancer before you know it? ›
If you're wondering how long you can have cancer without knowing it, there's no straight answer. Some cancers can be present for months or years before they're detected. Some commonly undetected cancers are slow-growing conditions, which gives doctors a better chance at successful treatment.Does exercise help fight cancer? ›
Studies strongly suggest that exercise lowers the risk for seven forms of cancer: bladder, breast, colon, endometrial, esophageal, kidney, and stomach. There are also intriguing clues that exercise helps prevent lung, blood, head and neck, ovarian, pancreatic, and prostate cancers, too.Can cancer be caused by poor diet? ›
Research has shown that poor diet and not being active are key factors that can increase a person's cancer risk.Which type of cancer is hereditary? ›
Examples of hereditary cancer syndromes are hereditary breast and ovarian cancer syndrome, Li-Fraumeni syndrome, Cowden syndrome, and Lynch syndrome. Also called family cancer syndrome and inherited cancer syndrome.Can Lysol cause cancer? ›
Lysol Disinfectant Spray (Reckitt & Colman. Inc.) Labeled or Unlabeled Toxic Ingredient: ORTHOPHENYLPHENOL (OPP): Carcinogenic; irritant.Does bleach cause cancer? ›
Long-term exposure to low levels of chlorine gas could cause permanent lung disease such as bronchitis and shortness of breath. It can also cause tooth corrosion. Long-term exposure is mostly found in the workplace. No cancer or reproductive effects have been reported from chronic exposure to chlorine.
Cancer survival rates by cancer type
The cancers with the lowest five-year survival estimates are mesothelioma (7.2%), pancreatic cancer (7.3%) and brain cancer (12.8%). The highest five-year survival estimates are seen in patients with testicular cancer (97%), melanoma of skin (92.3%) and prostate cancer (88%).
A cancer can grow into,or begin to push on nearby organs, blood vessels, and nerves. This pressure causes some of the signs and symptoms of cancer. A cancer may also cause symptoms like fever, extreme tiredness (fatigue), or weight loss. This may be because cancer cells use up much of the body's energy supply.Which is an early common symptom of cancer? ›
Extreme fatigue that doesn't get better with rest can be an early sign of cancer. Cancer uses your body's nutrients to grow and advance, so those nutrients are no longer replenishing your body. This “nutrient theft” can make you feel extremely tired.Does cancer show up in routine blood work? ›
Most blood tests aren't used on their own to diagnose cancer. But they can provide clues that may lead your health care team to make the diagnosis. For most types of cancer, a procedure to remove a sample of cells for testing is often needed to be sure.Can you just know if you have cancer? ›
Spotting signs of cancer
Changes to your body's normal processes or unusual, unexplained symptoms can sometimes be an early sign of cancer. Symptoms that need to be checked by a doctor include: a lump that suddenly appears on your body. unexplained bleeding.
“Cancer rules the chest, stomach, womb, and breasts, which means that a positive attitude to the body, reproduction, and parenting—your own or other children—is key,” Faulkner says.
Sometimes, a cancer diagnosis comes out of the blue, with no symptoms at all. But more often, there are various symptoms that may be warning signs of the disease.What cancers can you have without knowing? ›
Silent cancers are cancers that do not have any noticeable early symptoms. Some silent cancers include breast cancer, ovarian cancer, colorectal cancer, Pancreatic cancer and lung cancer.When should you suspect cancer? ›
But it's important to be aware of the common signs and symptoms of cancer. These can include: An unusual lump or swelling, especially in the neck, breast, belly, or testicle. Unexplained tiredness and loss of energy.What does cancer fatigue feel like? ›
People with cancer might describe it as feeling very weak, listless, drained, or “washed out” that may decrease for a while but then comes back. Some may feel too tired to eat, walk to the bathroom, or even use the TV remote. It can be hard to think or move.
Sadness and Depression. Many people with cancer feel sad. They feel a sense of loss of their health, and the life they had before they learned they had the disease. Even when you're done with treatment, you may still feel sad.