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What causes cancer? Diagnosis, prevention, and treatment

Medically reviewed by Gerardo Sison, Pharm.D.
Licensed Pharmacist
Updated Apr. 10, 2024  •  Published Aug. 7, 2023
Fact Checked
What causes cancer? Diagnosis, prevention, and treatment

Overview: What is cancer?

Cancer is caused by gene mutations in cells that disrupt their normal cycle and cause them to grow uncontrollably. While some cancers remain at their original site for a time, others may spread or metastasize to other parts of the body, which often makes cancer fatal and complicates treatment. 

While some cancers are caused by abnormal genes people are born with, most cancers are caused by acquired mutations in cellular genes that arise during our lifetime. Many people think of cancer causes as anything that damages genes, such as tobacco smoke or UV radiation. However, not all gene damage leads to cancer. 

The body has specific processes to repair DNA and eliminate abnormal cells. Sometimes the body doesn’t always succeed at stopping abnormal cells, especially in older people. When the defenses fail, cancerous cells can gain the advantage, leading to the development of cancer. 

RELATED: 9 things you can do to prevent cancer

Key takeaways:

  • Cancer is a common health condition that can affect anyone regardless of age, sex, race, or ethnicity. 

  • Cancer is caused by genetic changes that are either inherited, random, or caused by prolonged damage to cellular genes.

  • Risk factors for cancer may include age, family history of cancer, lifestyle, environmental exposures, certain viral infections, certain genetic disorders, certain medical conditions, and radiation. 

  • Symptoms of cancer will depend on the type of cancer and may overlap with symptoms of other health conditions. Potential signs and symptoms may include fatigue, feeling sick, weight changes (usually weight loss), the formation of a lump, pain, fevers, night sweats, bleeding, and digestive system problems. 

  • Cancer usually requires a medical diagnosis.

  • Cancer generally requires treatment. It may or may not resolve with treatment over a variable timeline. Even if the cancer is successfully treated, ongoing preventive measures may be required for many years, decades, or even the rest of a person’s life.

  • Treatment of cancer may include chemotherapy, immunotherapy, biologic therapy, targeted drug therapy, radiation therapy, surgery, and bone marrow transplant. 

  • Cancer is not always preventable, but the risk may be lowered by making certain lifestyle changes, maintaining a healthy weight, eating a healthy diet, and reducing exposure to carcinogens or certain types of radiation. 

  • Save on cancer treatments like Platinol (cisplatin), Soltamox (tamoxifen), (Adriamycin) doxorubicin, Trexall (methotrexate), and Xeloda (capecitabine) with free SingleCare discount cards.

What causes cancer?

Cancer is caused by genetic mutations that affect the way the body’s cells divide and form new cells. These genetic changes may affect only a few cells, but that can be enough to promote the growth of cancer. 

Cancer causes include:

  • Genetic problems that are inherited, but these aren’t often the main cause of childhood cancers, which typically stem from early or prenatal genetic mutations

  • Damage to cellular genes due to exposure to chemicals, radiation, inflammation, or viral infections

  • Errors that occur when cells copy their genes to grow new cells

Risk factors for cancer

Several factors may increase the risk of developing cancer. These include inheriting specific genes, being exposed to cancer-causing substances (carcinogens), radiation exposure, viral infections, obesity, and conditions that cause inflammation.

A family history of cancer is a highly predictive risk factor for certain types of cancer. Specific genes associated with cancer have been identified, such as BRCA1 and BRCA2 for breast cancer and APC for colorectal cancer. Being born with those genes does not make cancer certain, but it may increase the risk. Genetic testing can identify if a person has certain cancer risks.

Repeated exposure to carcinogens like tobacco smoke, asbestos, or radon is another prominent risk factor. For instance, people who smoke are 15 to 30 times more likely to get lung cancer than people who don’t. The number of carcinogens we encounter every day is almost uncountable. For instance, cigarette smoke has at least 70 known carcinogens. 

Certain types of radiation directly damage the DNA in the body’s cells. The most common DNA-damaging radiation that people are exposed to is ultraviolet rays from sun exposure or tanning beds. UV radiation is responsible for 93% to 96% of melanoma cases.

Viral infections may also raise the risk of developing cancer. Viruses infect the body’s cells and can insert their genetic information into a cell’s DNA, which may result in cancerous cells. The most common viral infections associated with cancer include human papillomavirus (HPV), Epstein-Barr virus (mononucleosis), HIV/AIDS, hepatitis B, and hepatitis C, among others.

Inflammation may also be linked to genetic changes that lead to cancer, particularly chronic inflammation due to autoimmune disorders. One consequence of inflammation is the buildup of reactive oxygen molecules, also known as free radicals. These molecules can directly damage the DNA in human cells, which may cause a mutation that leads to cancerous growth.

Obesity increases the risk of cancer for several reasons, including chronic inflammation. Around 4% to 8% of new cancer cases are linked to excess body weight. Being overweight may not only increase the risk of cancer, but it may also increase the risk of dying from cancer, according to cancer research.

Lifestyle is not a cause of cancer, but it is highly predictive of cancer risk. Through lifestyle and habits, people may expose themselves to carcinogens, radiation, viral infections, or inflammation that can damage cellular DNA. Lifestyle factors may include poor diet, physical inactivity, smoking, and alcohol consumption.

Is cancer serious? When to see a doctor

Cancer is a serious medical condition that requires diagnosis and treatment. While some types of cancer are less aggressive than others, even precancerous cells should be closely observed. If you notice any signs of cancer, such as unexplained weight loss, persistent fatigue, or unusual skin growths, make an appointment with a healthcare provider. 

Even if there aren’t symptoms, routine cancer screening can detect some cancers, such as breast cancer, skin cancer, colon cancer, and cervical cancer, at a precancerous or early stage. A healthcare provider or a family doctor can help determine if screening is necessary. 

How is cancer diagnosed?

A cancer diagnosis can be a complicated process. In most cases, people will be diagnosed by a specialist in oncology (cancer treatment) or other medical specialty. Diagnosis starts with a medical history and a physical examination. Be prepared to discuss symptoms and any family history of cancer. 

A number of tests may be necessary, including:

  • Blood tests that look for substances that appear in the blood when a person has cancer

  • Imaging of the affected area, including X-rays, CT scans, MRI scans, PET scans, or ultrasound

  • Biopsies to look at the cells under the microscope 

A major part of the diagnosis is determining what stage the cancer is in. Treating a later stage cancer may be a more involved process that includes surgery and the removal of nearby lymph nodes. The cancer stage, ranked from 0 to 4, can help determine the most appropriate treatment. 

  • Stage 0: this is the beginning of cancer—there are only a few abnormal cells, and the cancer hasn’t invaded other areas

  • Stage I: this is usually a small cancer or tumor that has not grown deeply into nearby tissues

  • Stage II: the cancer is larger but still located in the organ or tissues where it started

  • Stage III: the cancer cells have spread deeply and may have grown into surrounding organs or tissue; some of the cancer cells may be located in nearby lymph nodes

  • Stage IV: the cancer has metastasized, that is, spread to other parts of the body that are not near the source of the cancer

This staging system applies broadly across many types of cancers, but there can be important differences depending on specific types of cancer, such as leukemia or myeloma. Each type can be staged using additional criteria (like tumor size, location, cell type, etc.). Always consult with a healthcare professional for specifics related to each case.

Is cancer hereditary?

Cancer is closely linked to genetics. People with a family history of cancer are more likely to develop cancer than others. Some of the genes associated with cancer have been identified. These genes do not cause cancer, but they may raise the risk of developing certain types of cancer. People can be tested for these genes and screened regularly throughout their lives.

Is cancer curable?

Cancer is curable in most cases, but it depends on the type of cancer and how advanced it is. However, no one can be sure if all cancerous cells are cleared from the body when treatment succeeds. There is always a risk of recurrence, so preventive treatment for months, years, or decades is often part of the cure.

Treatments will depend on the type of cancer, the stage of the cancer, and aspects of one’s medical condition. The most common treatments are:

  • Chemotherapy

  • Immunotherapy

  • Biologic drugs

  • Targeted therapy

  • Hormone therapy

  • Radiation therapy

  • Surgery

  • Bone marrow transplant

Cancer care may include other treatments such as anti-nausea medications or over-the-counter antidiarrheal drugs or laxatives to reduce or manage the side effects of cancer drugs or therapies.

RELATED: Does Medicare cover cancer treatment?

How to prevent cancer

Because there are so many ways that cells can be damaged or changed into cancerous cells, preventing cancer can be involved and complex. Cancer prevention is not 100% guaranteed. Many risk factors, such as genetics, are out of people’s control. However, about 4 out of every 10 cancer cases are associated with things that can be changed. Here are some risk factors that may be within our control: 

  • Eat a healthy diet rich in vegetables and fruits

  • Maintain an optimal bodyweight

  • Engage in regular physical activity

  • Manage chronic conditions 

  • Stop smoking andvoid exposure to second-hand smoke

  • Avoid alcohol, highly processed foods, red meats, and processed meats

  • Protect your skin from excessive sun exposure with protective clothing or high-SPF sunscreen

Most importantly, get regular checkups and cancer screenings

Regular checkups and screenings are one of the most efficient ways to avoid cancer. At every wellness check or doctor’s visit, tell the clinician about any issues or symptoms that concern you. If something unusual happens, such as unexplained weight loss, sensory changes, an unexpected lump, or a new growth on the skin, see a healthcare professional. Get regular screening tests done based on the medical advice of a healthcare provider. Early detection through screening saves lives. Finally, genetic testing can help identify a risk for cancer when there’s still plenty of time to take cancer prevention measures.

RELATED: Love the skin you’re in: the importance of annual skin cancer checks

FAQs about cancer causes

What causes pancreatic cancer?

Like all other cancer types, pancreatic cancer is caused by changes in the genes of cells in the pancreas. Risk factors that may contribute to the development of cancerous pancreatic cells include inherited genes, smoking, diabetes, obesity, and chronic pancreatitis. Some studies also suggest a potential correlation between exposure to dry cleaning chemicals and an increased risk of pancreatic cancer.

What causes prostate cancer?

The major risk factors for prostate cancer are age, race, and a family history of prostate cancer. None of these directly cause prostate cancer, but they may play a part in its development. For the most part, genetics play a big part in the development of prostate cancer. Modifiable risk factors that may increase the risk of prostate cancer include smoking, obesity, and high consumption of calcium.

RELATED: How your diet affects your prostate health

What causes colon cancer?

As with many cancers, the major risk factors for colon cancer are out of people’s control, such as age, family history of colorectal cancer, inherited inflammatory bowel disease, and genetic disorders. However, there are controllable risk factors that may contribute to the development of colon cancer, including being overweight, tobacco use, physical inactivity, and a high-fat, low-fiber diet. Regularly eating processed meats may also increase the risk of colon cancer.

RELATED: Colon cancer treatments and medications

What’s next? Additional resources for people with cancer

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Medically reviewed by Gerardo Sison, Pharm.D.
Licensed Pharmacist

Gerardo Sison, Pharm.D., graduated from the University of Florida. He has worked in both community and hospital settings, providing drug information and medication therapy management services. As a medical writer, he hopes to educate and empower patients to better manage their health and navigate their treatment plans.

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