Let's Talk About the Causes of Cancer

Empowering stat: 42% of new cancers are preventable. Learn what factors you can control for a healthier life ahead.

So here’s a question you might have—what causes cancer in the first place? And is there anything you can do to prevent getting the disease? Well, yes. While you can’t bring your chances of a diagnosis to zero (if only!), there’s plenty to know about what causes cancer and ways to reduce your risk. Read on for the knowledge you need to stay as healthy as you can.

Causes of Cancer

Our Pro Panel

We asked the nations top cancer experts for the most up-to-date-information possible.

Steven Edge, M.D. headshot.
Stephen Edge, M.D.

Stephen Edge, M.D.

Surgical Oncologist and Vice President

Healthcare Outcomes and Policy Roswell Park Comprehensive Cancer Center

Buffalo, NY

Josephine (Joy) Feliciano, M.D. headshot.
Josephine (Joy) Feliciano, M.D.

Josephine (Joy) Feliciano, M.D.

Medical Oncologist, Assistant Professor of Oncology

The Johns Hopkins University School of Medicine

Baltimore, MD

Marleen I. Meyers, M.D.
Marleen I. Meyers, M.D.

Marleen I. Meyers, M.D.

Medical Oncologist, Clinical Associate Professor, Department of Medicine, and Director of Perlmutter Cancer Center Survivorship Program

NYU Langone Health

New York, NY

Cancer Causes
Frequently Asked Questions
What in cigarettes causes cancer?

It’s not nicotine, as you might think. While alkaloid nicotine is the addictive part of tobacco, it’s not a known carcinogen. That honor goes to more than 60 well-established carcinogens in one cigarette. Remember that a carcinogen is a cancer-causing substance, so you’re breathing in toxicity with each puff. Here are just some of the chemical classes of carcinogens found in cigarette smoke: polycyclic aromatic hydrocarbons (PAHs), N-nitrosamines, aromatic amines, aldehydes, volatile organic hydrocarbons, and metals.

What foods cause cancer?

It’s tough for researchers to find hard and fast links between food and cancer risk for a host of reasons, including how some foods include nutrients that might both lower and raise risk, so it’s good to be cautious about assigning cancer risk to food. What we do know: Processed meat in any amount and more than about 18 ounces of fresh meat per week were most strongly linked with a higher risk of cancer.

Does drinking alcohol cause cancer?

Here’s the deal on alcohol and cancer: It’s one of the few substances consistently linked to an increased risk of cancer (tobacco is another). What you drink doesn’t seem to make much of a difference, either. Researchers don’t yet know why this link exists, but they have ideas. Two chemicals in alcohol, ethanol and acetaldehyde, can cause damage to the DNA of healthy cells. By abstaining or limiting the number of drinks you have, you can lower your risk. Women: Drink no more than one drink per day. Men: Drink no more than one to two drinks a day.

What STD causes cervical cancer?

High-risk types of human papillomavirus (HPV) can cause cervical cancer in women, according to the National Institutes of Health. HPV infections can happen to men too, and lead to penile cancers. HPV can also cause cancers of the mouth, throat, and anus in both women and men. Use a condom and lower your risk for all!

What’s Cancer Anyway? Let’s Recap

Before examining the causes of cancer, let’s get clear on what the disease actually is: Cancer comes to be when abnormal cells grow out of control, anywhere in your body, due to mutations in our cells’ DNA. While normal cells divide, get older and die in a predictable fashion, copying DNA as they go, cancer cells are rebels without a cause. They don’t die, and instead, mutate, replicate and form tumors.

Where these cells start growing—the primary site of your cancer—determines the type of cancer you have. When those cells spread through your blood or lymphatic system (the network of tissues and organs that flush out toxins, waste, and all sorts of undesirables), the areas they invade are called metastatic sites.

One thing to note: A cell can be abnormal without necessarily being cancerous (also known as malignant). Rather, it could be benign (not cancer), or precancerous or premalignant (likely to become cancer). Cancer screening and testing enables doctors to investigate exactly what you’re dealing with.

How Do People Get Cancer?

You understand that cancer develops when abnormal cells grow out of control, invading parts of the body where they shouldn’t, but why do they start doing that? How do cancer cells come to be?

Cancer, put simply, is caused by changes—a.k.a. mutations— to our cells’ DNA. This can happen for two reasons: inherited mutations and acquired mutations. Let’s look at both more in-depth.

Inherited Cancer Causes: What’s in Your Family

About 5% to 10% of all cancers are inherited, known as familial or hereditary cancers. Many cancer mutations happen in the DNA of our genes, which is why you’ve heard so much about genetic factors. For instance, if you’re a woman with one first-degree female relative (sister, mother, daughter) diagnosed with breast cancer, your risk for breast cancer is doubled. If two first-degree relatives have been diagnosed, your risk is five times higher than average. Here are some common gene mutations:

BRCA1 and BRCA2

BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two) are tumor suppressor genes we all have. When those genes mutate—meaning they aren’t able to fix the cellular DNA as they should—you’re at a higher risk for different types of cancer, most notably breast cancer. The average woman in the U.S. has about a 1 in 8, or 12%, risk of developing breast cancer in her lifetime, while those with the BRCA1 and BRCA2 gene mutations (either one, or both) have up to a 72% risk.

Angelina Jolie stirred up controversy when she wrote about her preventative double mastectomy in The New York Times in 2013. Her reason for surgery? She has an inherited genetic mutation in the BRCA1 gene. But men with BRCA1 and BRCA2 mutations are also at risk of breast cancer. Singers Beyoncé Knowles-Carter and Solange Knowles’ father, Mathew Knowles, revealed he has the BRCA 2 mutation and had breast cancer in October 2019. Men with these gene mutations are at a higher risk of breast cancer than men without, at eight times greater than average.

Women with these gene mutations are also at higher risk than the generation population for ovarian cancer. More numbers: For women without these mutations, about 1.3% will develop ovarian cancer in their lifetime. In women with the BRCA1 mutation, about 44% will develop the disease by 80; in women with the BRCA2 mutation, 17%. Other cancers that women and men with these mutations are potentially at higher risk for include:

Men with BRCA1 or 2 genetic mutations are at higher risk for prostate cancer, too. Those with mutated BRCA1 genes are at slightly higher risk, while those with the BRCA2 mutation are seven times more likely to develop prostate cancer than men with the normal gene.

This isn’t the only kind of inherited genetic mutation, and researchers are studying other possible mutations that cause cancer.

Lynch Syndrome

Lynch syndrome (also called hereditary non-polyposis colorectal cancer) can be caused by a mutation in what’s known as mismatch repair (MMR) genes MLH1, MSH2, PMSI, and PMS2. This syndrome puts you at higher risk for developing a long list of cancers:

  • Colorectal cancer (especially before age 50)

  • Endometrial cancer

  • Ovarian cancer

  • Stomach cancer

  • Small intestine cancer

  • Pancreatic cancer

  • Kidney cancer

  • Brain cancer

  • Ureters cancer

  • Bile duct cancer

Li-Fraumeni Syndrome

Another syndrome to know: Li-Fraumeni syndrome. It’s rare, but associated with a higher risk for sarcoma (a rare cancer that grows in connective tissue like muscles, fat and blood vessels), including osteosarcoma and soft-tissue sarcomas. It’s also linked to:

  • Leukemia

  • Brain cancers

  • Cancer of the adrenal cortex

  • Breast cancer

Inherited mutations connected to this syndrome include the TP53 gene and CHEK2 gene, both tumor suppressor genes.

Familial Melanoma

When two or more first-degree relatives are diagnosed with melanoma, it’s known as familial melanoma. The inherited condition has been linked to two genes, CDKN2A and CDK4, but other genes could be at play, because these don’t account for all cases of familial melanoma.

Why does this all matter? Because knowing if you have an inherited mutation linked to cancer can help predict if you’re at an increased risk for the disease. That can help you get diagnosed in earlier stages, when treatment success rates are higher. However, for this knowledge to make a difference, you of course need to be tested for genetic mutations before you suspect cancer. Ask your doctor if it makes sense for you to be tested, particularly if you believe you’re in a high-risk group.

Acquired Cancer Causes: What Happens During Your Lifetime

The rest of cancers that are diagnosed—about 90% to 95%—are caused by genetic mutations that crop up as we live our lives, sometimes by exposure to carcinogens (anything known to cause cancer). Experts call these cancers non-hereditary or spontaneous cancers.

The good news? Through simple (though definitely not always easy) lifestyle changes, you can help reduce your exposure to carcinogens and slash your cancer risk.

If you think it’s too late for any healthier-living upgrades you adopt to have an impact, know this: Even making lifestyle changes during cancer treatment can be helpful in reducing your risk of recurrence, according to the Centers for Disease Control and Prevention (CDC), as well as making you as strong as possible for cancer treatment. So it’s rarely too late to change for the better.

What Cancer Risk Factors Should I Know About?

So what factors hike up your chances of getting cancer? Here’s one none of us can do much about: Getting older. Approximately 80% of all cancers in the U.S. are diagnosed in people 55 years of age or older. But don’t throw up your hands and cry uncle: At least 42% of newly diagnosed cancers in the U.S. (about 740,000 cases in 2019) might be preventable, researchers have found. The biggest contributors? About 19% of all cancers are caused by smoking and 18% triggered by a dangerous combo of excess weight, physical inactivity, excess alcohol consumption, and poor nutrition.

Let’s look at these causes more closely, courtesy of the National Cancer Institute (NCI):

Lifestyle Causes

  • Alcohol Use. Even light drinkers (those who have no more than one drink per day) as well as binge drinkers (considered four or more drinks for women, and five or more drinks for men, in one sitting, in about two hours) have a modestly increased risk of some cancers. Alcohol could be a factor in the following cancers:

  • Tobacco Use. File under Things You Already Knew: Smoking increases your risk for cancers, including lung cancer. It isn’t the nicotine that’s the problem, either: It’s just one of many, many chemicals in tobacco and some of those, including tar, are known carcinogens. Turns out, nicotine isn’t! Cigarette smoke itself contains high levels of acrolein, a chemical that’s toxic to the lungs, which is why secondhand smoke is dangerous too.

  • Obesity. Being overweight may put you at an increased risk of several types of cancer. These include:

    • Breast cancer (in post-menopausal women)

    • Colon cancer

    • Rectal cancer

    • Endometrial cancer (lining of the uterus)

    • Esophageal cancer

    • Kidney cancer

    • Pancreas cancer

    • Cancer of the gallbladder

Environmental Causes

  • Cancer-causing Substances. We’re exposed to carcinogens in the form of environmental toxins, such as asbestos or benzene, that can lead to a variety of cancers, including lung cancer.

  • Radiation. Have you seen the award-winning HBO miniseries Chernobyl, about the nuclear accident in 1986 in Ukraine that released radioactive material into the air? Then you’ll have seen evidence of what radiation can do to the body, including causing cancers of the thyroid and bladder.

  • Sun exposure. It’s why we slather on sunscreen and try to avoid basking when the ultraviolet rays are at their most intense: To prevent skin cancer. You skin tans or freckles to absorb the UV rays and protect their cells’ DNA from damage, but the damage can still occur. When it does, compromised cells grow out of control, resulting in melanoma (the deadliest of all skin cancers), basal cell carcinoma or squamous cell carcinoma, depending on the affected cell.

Sex-Based Causes

  • Hormones. Did you know that estrogens, a type of female sex hormones, are known human carcinogens and make women more susceptible to certain types of cancer? You may be familiar with the potential link between hormone replacement therapy (HRT) and estrogen-dependent cancers, like estrogen receptor (ER) positive breast cancer. The relationship between the two has been a source of controversy, even after findings from the Women’s Health Initiative Hormone Trials, a large prospective study on the topic, were published in the early 2000’s. Results showed that HRT resulted in:

    • A 26% increase in breast cancers

    • No effect on endometrial cancer

    • A 37% reduction in colon cancers

If you’re on this therapy or considering it, talk to your doctor about your risk factors.

Health-Based Causes

  • Chronic Inflammation. This can be brought on by chronic infection, abnormal immune reactions, or conditions such as obesity, the NCI reports, and can lead to several types of cancer.

  • Immunosuppression. People on immunosuppressive drugs (medications that weaken the immune system) or those that have HIV/AIDS are at increased risk for some cancers.

  • Infectious Agents. Infections such as Human Papillomaviruses (HPVs), Hepatitis B and Hepatitis C viruses, and Helicobacter pylori (H. pylori), among others, can cause cancer, including liver or stomach, respectively.

Does Your Diet Cause Cancer?

We’ve talked about environmental triggers as well as what you puff and drink, but how about what you put on your plate? Do some foods cause cancer?

The short answer: We don’t really know. It’s been tough for researchers to pinpoint specific links between food, nutrients, and cancer, for multiple multiple reasons, including:

  • A single food can contain substances that could both lower and increase risk, simultaneously.

  • We eat many different foods and drinks, creating interactions that pose challenges to research.

  • How much of a certain food you eat can change its impact in your body.

  • How food is prepared could influence its risk and benefits, too.

So as you can see, it’s not an avoid-these-5-foods-and-you’ll-be-fine situation when it comes to cancer risk. What we do know is that fruits and vegetables likely lower the risk of several cancer types, including:

  • Stomach Cancer

  • Lung Cancer

  • Prostate Cancer

And meat might be an issue: Eating processed meat (like sausages, salami, hot dogs, ham and bacon) in any amount and more than about 18 ounces of fresh meat per week were most strongly linked with a higher risk of cancer.

So What Can I Do to Prevent Cancer?

While there’s no method for cutting your cancer risk to zero, researchers and doctors have ID’ed ways that you can reduce your risk, including:

Get Screened

Making sure you get appropriate cancer screenings when you reach the recommended age is essential to finding cancer early, when it’s most treatable. Follow recommendations from the CDC for screenings, including those for breast cancer, cervical cancer, colorectal cancer and lung cancer.

Stop Smoking

Stubbing out the butts (with help if you need it, no shame there!) is vital to reducing your cancer risk. If you live with someone who smokes or you’re around secondhand smoke on a regular basis, reduce your exposure as much as possible.

Limit Drinking

Cut back your alcohol consumption to lower your risk. Dialing it down to about one drink per day for women, two for men, or cutting out alcohol altogether could be one of the best decisions you’ve ever made. A drink is defined as:

  • 12 ounces (oz) or 341 milliliters (ml) of beer

  • 5 oz or 142 ml of wine

  • 1.5 oz or 43 ml of 80-proof liquor

Lose Weight

If you’re overweight or obese, shedding pounds is an important step in cancer prevention. We don’t yet know why being overweight or obese could cause the disease, but it’s a known risk factor in a host of cancers.

Exercise Regularly

Get moving at least 30 minutes a day to help you stay fit as well as lose weight, both of which can keep your cancer risk in check. No need to go to extremes--brisk walking is great!

Eat a Healthy Diet

Think lots of fruits, vegetables, whole grains and lean proteins.

Limit Sun Exposure

Whatever the weather, year round, wear SPF 30 on your face and exposed areas of your body. Look for one that says broad spectrum, which means it shields skin from both UVA and UVB rays (both are linked to skin cancer). Try to avoid being in the sun between 10 a.m. and 4 p.m., when the rays are most intense.

Be Aware of Your Environment

If you live near or on an environmentally toxic site, or are exposed to toxic chemicals through your job, you should know about your possible exposure to known carcinogens. The United States Environmental Protection Agency (EPA) has a search function on their site, so you can get wise to Superfund sites (contaminated areas the EPA is working to clean up) near where you live.

Avoid Risky Behavior

These can include unsafe sex (wear a condom) and don’t share needles (and seek professional help for addiction), both of which can lead to increased risk for certain cancer types.

Even with following all these preventative measures, there’s no guarantee that you’ll never get cancer, but you will greatly reduce your risk. And you’ll feel a whole lot better, ensuring you live all the healthy days you’re given to the max—no better goal than that!

  • Inherited Cancers: American Cancer Society. (2018). Family Cancer Syndromes. cancer.org

  • BRCA1, 2 Genetic Mutation: Journal of Cancer. (2019). “BRCA Genes: The Role in Genome Stability, Cancer Stemness and Therapy Resistance,” ncbi.nlm.nih.gov

  • BRCA1, 2 Mutations and Men: BreastCancer.Org. Men With BRCA Mutations Have Much Higher Risk of Cancer. (2017). breastcancer.org

  • Familial Melanoma: Cancer.Net. (2018). Familial Malignant Melanoma. cancer.net

  • Mutated Genes: The European Molecular Biology Organization. (2013). “Function of oncogenes in cancer development: a changing paradigm,” ncbi.nlm.nih.gov

  • Cancer Prevention: Mayo Foundation for Medical Education and Research. (2020). Overview, Prevention. mayoclinic.org

  • Cancer Risk Factors: National Cancer Institute. (2015). Risk factors for cancer. cancer.gov

  • Age and Cancer Risk: American Cancer Society. Cancer Facts & Figures 2019. (2019). cancer.org

  • Alcohol and Cancer Risk: Cancer.Net. (2017). Alcohol. cancer.net.

  • Smoking and Cancer Risk: Sultan Qaboos University Medical Journal. (2013). “Tobacco Smoking and Lung Cancer: Perception-changing facts,” ncbi.nlm.nih.gov

  • More on Smoking and Cancer: Centers for Disease Control and Prevention (US); National Center for Chronic Disease Prevention and Health Promotion (US); Office on Smoking and Health (US). (2010). How Tobacco Smoke Causes Disease: The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General. ncbi.nlm.nih.gov

  • Weight and Cancer Risk: American Cancer Society. (2018). Does body weight affect cancer risk? cancer.org

  • Food and Cancer: Cancer.Net. (2019). Food and Cancer Risk. cancer.net

  • Cancer Screening Recommendations: Centers For Disease Control and Prevention. Screening Tests. cdc.gov/cancer/dcpc/prevention/screening.htm

  • Search for Superfund Sites: The Environmental Protection Agency (EPA). Search for Superfund Sites Where You Live. epa.gov/superfund/search-superfund-sites-where-you-live

Erin L. Boyle
Meet Our Writer
Erin L. Boyle

Erin L. Boyle, the senior editor at HealthCentral from 2016-2018, is an award-winning freelance medical writer and editor with more than 15 years’ experience. She’s traveled the world for a decade to bring the latest in medical research to doctors. Health writing is also personal for her: she has several autoimmune diseases and migraines with aura, which she writes about for HealthCentral. Learn more about her at erinlynnboyle.com. Follow her on Twitter @ErinLBoyle.