Cancer Awareness: The Complete Guide

Key numbers at a glance

What cancer is and why it develops

Cancer is not one disease but a large group of more than a hundred, linked by a single feature: cells that grow and divide without the normal controls. Every day your cells copy their DNA as they divide, and occasionally mistakes creep in. The body has strong systems for repairing those mistakes or removing damaged cells. Cancer develops when enough changes build up in one cell that it escapes those checks, keeps dividing, and in time invades nearby tissue or spreads elsewhere in the body.

Most of these changes are acquired during life rather than inherited. Some come from exposures that damage DNA, such as tobacco smoke, ultraviolet (UV) radiation and alcohol. Some come from infections, such as human papillomavirus (HPV) and hepatitis B and C. Many are simply the result of the random errors that happen as cells divide over decades, which is why age is the single biggest risk factor for most cancers. A minority, roughly 5 to 10 percent according to the American Cancer Society, are strongly linked to an inherited gene change.

Cancer is common. The American Cancer Society estimates that about 2 million people in the US are diagnosed each year, and roughly 4 in 10 Americans will be diagnosed with cancer at some point in their lives. But the picture has changed a great deal: death rates from cancer in the US have fallen substantially since the early 1990s, driven by less smoking, earlier detection and better treatment. There are now more than 18 million cancer survivors in the US.

Why stage matters

Doctors describe how far a cancer has grown and spread using a stage, usually from 1 to 4. An early-stage cancer is confined to where it started; a later-stage cancer has spread to lymph nodes or distant organs. For many common cancers, including colorectal, breast, cervical and melanoma, the outlook is much better when the cancer is found at an early stage, because surgery or other treatment is more likely to remove it completely. That single fact is why screening and prompt reporting of symptoms matter so much, and why this guide keeps coming back to both.

What raises and lowers your risk

Some risk factors cannot be changed: age, sex, family history and inherited gene changes. But a substantial share of US cancers are linked to factors that can be changed, and tobacco tops that list by a wide margin. According to the American Cancer Society, cigarette smoking accounts for about 3 in 10 cancer deaths in the US. Smoking causes not only lung cancer but cancers of the mouth, throat, esophagus, stomach, pancreas, kidney, bladder, cervix and blood. Quitting at any age lowers risk, and the benefit grows with every year you stay smoke-free.

After tobacco, the most important changeable factors are excess body weight, alcohol, physical inactivity, diet, UV exposure and certain infections. Excess weight is linked to many types of cancer, including colorectal, endometrial, kidney, pancreatic and post-menopausal breast cancer. Alcohol is linked to cancers of the mouth, throat, esophagus, liver, colon and breast, and no level of drinking is known to be free of cancer risk; the Dietary Guidelines advise that adults who drink limit themselves to 2 drinks a day or less for men and 1 or less for women, and drinking less is better for health than drinking more.

Lifestyle changes lower risk; they do not eliminate it. People who never smoked get lung cancer, and very fit people get colorectal cancer. That is not a reason to give up on prevention, but it is a reason never to dismiss a symptom because you live healthily. Prevention and early detection work together, and neither replaces the other. Think of healthy habits as shifting the odds in your favor, and of screening and prompt reporting as the safety net underneath.

• Do not smoke or use tobacco; if you do, ask your doctor about medicines and support, or call 1-800-QUIT-NOW
• If you drink alcohol, drink less; not drinking is best for cancer prevention
• Aim for at least 150 minutes of moderate activity a week, and sit less
• Eat plenty of vegetables, fruit, whole grains and beans, and limit processed and red meat and sugary drinks
• Protect your skin with shade, clothing and broad-spectrum sunscreen of SPF 30 or higher, and never use indoor tanning
• Get the HPV and hepatitis B vaccines as recommended

Vaccines and infections that can lead to cancer

Several cancers start with an infection, which means vaccines and testing can prevent them. HPV is the clearest example. It causes almost all cervical cancers and a large share of cancers of the throat, anus, penis, vagina and vulva. The HPV vaccine can prevent most of the cancers HPV causes. The CDC recommends routine vaccination at age 11 or 12, and it can start as early as 9. Children who start before their 15th birthday need two doses; people who start at 15 or older need three. Catch-up vaccination is recommended through age 26, and adults aged 27 to 45 can discuss it with their doctor.

Hepatitis B and hepatitis C infections can cause long-term liver damage and liver cancer. The hepatitis B vaccine is recommended for infants, and the CDC also recommends it for many adults who were never vaccinated; ask your doctor whether you need it. There is no vaccine for hepatitis C, but the CDC recommends that every adult be tested at least once, and that pregnant people be tested during each pregnancy, because modern treatment can cure most infections and so lower future liver cancer risk.

A stomach infection called Helicobacter pylori is linked to stomach cancer and is treatable with antibiotics, and HIV raises the risk of several cancers, which effective treatment helps reduce. Both of these are common, often cause no symptoms for years, and are easy to test for. If you have been diagnosed with any of these infections, ask your doctor whether it changes your cancer screening or follow-up, since some people with long-term hepatitis need regular liver checks.

Warning signs worth reporting

Most symptoms that can signal cancer turn out to be something else. That is precisely why people delay: they reasonably assume it is nothing. The point of reporting a symptom is not to assume the worst but to let a clinician rule things out. The features that should prompt a visit are persistence, change and a lack of explanation. A cough after a cold that settles in two weeks is ordinary; a cough that lasts for weeks, or keeps getting worse, needs checking.

Pain is a poor guide. Many early cancers cause no pain at all, and a painless lump is not less concerning than a painful one. Bleeding from anywhere it should not occur deserves attention, including blood in the urine, blood in the stool, coughing up blood, and vaginal bleeding after menopause or between periods. Unexplained weight loss, meaning losing weight without trying, is always worth reporting, as is persistent unexplained fatigue.

When you see your doctor, say plainly if you are worried about cancer. It is useful information, not an overreaction. Be specific about when the symptom started, how it has changed and what makes it better or worse. A short written note helps, because it is easy to forget details in the appointment. If the first explanation does not fit or the symptom continues, go back; it is appropriate to ask what the next step would be.

• A new lump or thickening anywhere, including in the breast, testicle, neck or armpit
• A cough that does not go away, or hoarseness lasting more than a few weeks
• A lasting change in bowel or bladder habits
• Blood in the stool or urine, coughing up blood, or bleeding after menopause
• A sore that does not heal, including in the mouth, or a white or red patch inside the mouth
• A mole or spot that is new, changing or different from your others
• Difficulty swallowing, persistent indigestion or heartburn that is new for you
• Unexplained weight loss, fevers or drenching night sweats

Cancer screening: what US guidelines recommend

Screening means testing people who have no symptoms, to find cancer early or to find precancerous changes that can be removed before they become cancer. The US Preventive Services Task Force (USPSTF) reviews the evidence and recommends screening only where the benefits clearly outweigh the harms. Those harms are real: false alarms that lead to anxiety and further tests, and overdiagnosis, which means finding slow-growing cancers that would never have caused a problem. That is why screening is recommended for specific ages and intervals, and not for everyone, all the time.

Under the Affordable Care Act, most private health plans must cover USPSTF-recommended screenings with an A or B grade without a copay or deductible when you see an in-network provider. Medicare covers the main cancer screenings too. If cost worries you, call your insurer or ask your doctor's office before the test, and ask whether any follow-up test would also be covered. Free or low-cost breast and cervical screening is available to eligible people through the CDC's National Breast and Cervical Cancer Early Detection Program.

A normal screening result is reassuring, but it applies only to that test on that day. It does not cover you if you later develop symptoms, and no screening test catches every cancer. If you notice a warning sign between screenings, report it rather than waiting for your next scheduled test. Screening and symptom checks are separate tools that do different jobs.

Colorectal cancer

The USPSTF recommends screening for adults aged 45 to 75, and individual decisions for those 76 to 85. There are several good options. A stool test such as the fecal immunochemical test (FIT) is done at home once a year; a stool DNA-FIT test is done every 1 to 3 years; a colonoscopy, if normal, is usually repeated every 10 years; and CT colonography or flexible sigmoidoscopy are other choices. The best test is the one you will actually complete. Any abnormal stool test must be followed by a colonoscopy, or the screening has not done its job. People with a strong family history, inflammatory bowel disease or certain inherited syndromes may need to start earlier.

Breast, cervical, lung and prostate cancer

For breast cancer, the USPSTF recommends a mammogram every 2 years for women aged 40 to 74. Women at higher risk, including those with a strong family history or a known gene change, may need earlier or additional imaging. For cervical cancer, screening runs from 21 to 65: a Pap test every 3 years from 21 to 29, and from 30 to 65 either a Pap test every 3 years, an HPV test every 5 years, or both together every 5 years. Screening is usually not needed after 65 if earlier results were normal, or after a hysterectomy with removal of the cervix for non-cancer reasons.

For lung cancer, the USPSTF recommends a yearly low-dose CT scan for adults aged 50 to 80 who have a 20 pack-year smoking history and still smoke or quit within the past 15 years. A pack-year is one pack a day for a year, so 20 pack-years could be a pack a day for 20 years or two packs a day for 10. For prostate cancer, PSA screening for men aged 55 to 69 is an individual decision to make with your doctor after weighing the possible benefit against the risk of overdiagnosis and treatment side effects; routine screening is not recommended at 70 and older. Black men and men with a family history have a higher risk and may want to discuss screening earlier.

Skin, colorectal and breast cancer up close

Skin cancer is the most common cancer in the US, and almost all of it is linked to UV exposure from the sun or tanning beds. Melanoma is less common than the other types but more serious. Found early, it is usually highly treatable with simple surgery. The ABCDE guide helps you spot a mole worth checking: Asymmetry, an irregular Border, uneven Color, a Diameter larger than about 1/4 inch (6 mm), and, most important, Evolving, meaning change in size, shape or color. Other skin cancers often look like a sore that does not heal, or heals and comes back, or a shiny or scaly patch.

Colorectal cancer is one of the most common cancers in the US, and rates in adults under 50 have been rising for reasons that are not yet fully understood. Symptoms include a lasting change in bowel habits, blood in or on the stool, abdominal pain, unexplained weight loss and iron-deficiency anemia. Rectal bleeding is often put down to hemorrhoids, and frequently it is, but it should still be checked, especially if it is new. Screening can find and remove polyps before they ever become cancer.

Breast cancer is the most common cancer in US women apart from skin cancer, and men can develop it too, though far less often. Know how your breasts normally look and feel, and report a new lump or thickening, a change in size or shape, skin dimpling, a newly inverted nipple, nipple discharge, a rash around the nipple, or persistent pain in one area. Most breast changes are benign, but all need checking, and a recent normal mammogram is not a reason to wait.

Family history and inherited risk

Most cancers are not caused by an inherited gene change. Cancer is common, so many families will have more than one case simply by chance. But some patterns suggest an inherited risk: several close relatives on the same side of the family with the same or related cancers, cancers diagnosed at a young age, usually under 50, a relative with more than one type of cancer, breast cancer in a man, or ovarian cancer at any age. The best-known inherited conditions are changes in the BRCA1 and BRCA2 genes, linked to breast, ovarian, prostate and pancreatic cancer, and Lynch syndrome, linked to colorectal, endometrial and several other cancers.

The USPSTF recommends that primary care clinicians assess women with a personal or family history of breast, ovarian, tubal or peritoneal cancer, or with ancestry associated with BRCA gene changes, and refer those with a positive assessment for genetic counseling and, if appropriate, testing. Genetic counselors explain what a test can and cannot tell you before you take it, and what a result would mean for you and your relatives.

A positive result can change a great deal: when screening starts, how often it happens, which tests are used, and whether preventive medicines or surgery are worth discussing. A negative result in a family with a known gene change can be very reassuring. Direct-to-consumer genetic tests look at only a small number of changes and can miss many that matter, so they are not a substitute for counseling and clinical testing.

• Write down a family tree covering both sides, with each cancer type and the age at diagnosis
• Include parents, siblings, children, grandparents, aunts, uncles and cousins where you can
• Ask your doctor whether your pattern warrants genetic counseling
• If a gene change is found, share the result with relatives; it affects their risk too

If you are diagnosed: treatment and side effects

A cancer diagnosis brings a rush of information at a time when it is hardest to absorb. It helps to know the main treatment types. Surgery removes the tumor. Radiation therapy uses targeted high-energy beams to damage cancer cells. Chemotherapy uses medicines that kill fast-dividing cells. Targeted therapies act on specific features of cancer cells, hormone therapies block hormones that some cancers rely on, and immunotherapy helps the immune system recognize and attack cancer. Many people receive a combination. It is entirely reasonable to ask for a second opinion, and most cancer doctors expect it.

Side effects depend on the treatment and vary widely between people. Common ones include fatigue, nausea, hair loss, mouth sores, skin reactions in the radiation area, and a lowered resistance to infection. Many can be managed well: anti-nausea medicines often work best when taken on schedule rather than only once nausea starts. Immunotherapy can cause inflammation in almost any organ, sometimes weeks or months after a dose, so tell any clinician you see, including in the emergency room, that you are receiving it.

One side effect is an emergency. Chemotherapy can lower the white cells that fight infection, and an infection in that state can become life-threatening within hours. If you have a temperature of 100.4°F (38°C) or higher during or shortly after chemotherapy, call your cancer care team right away, using their 24-hour number, and go to the emergency room if you cannot reach them. Do not wait to see whether it settles, and do not take a fever reducer to bring it down before calling.

• Keep your cancer care team's 24-hour number in your phone and wallet
• Check with your team before taking any over-the-counter medicine, supplement or herbal product
• Report new symptoms early rather than waiting for your next appointment
• Ask about clinical trials; the National Cancer Institute lists trials across the US

Life after treatment and support for families

The end of treatment is often harder than people expect. The regular appointments and the sense of actively fighting stop, while the body and mind are still recovering. Many survivors live with late effects such as fatigue, problems with thinking and memory, numbness from nerve damage, lymphedema, early menopause, fertility changes, and heart or lung effects from some treatments. Fear that the cancer will come back is very common. Low mood and anxiety after treatment ends are common too and treatable, so mention them.

Ask your team for a survivorship care plan: a written summary of the treatments you had, the late effects to watch for, and your follow-up schedule. Share it with your primary care doctor. Cancer-related fatigue often improves more with gradual, regular physical activity than with prolonged rest, so build up slowly in the way your care team advises. The American Cancer Society runs a helpline at 1-800-227-2345, available 24 hours a day, and the National Cancer Institute offers information on financial, practical and emotional support.

If someone you know has cancer, the most helpful thing is to stay in touch. Many people with cancer say that friends drifting away, often for fear of saying the wrong thing, was among the most painful parts. You do not need perfect words. Listen, follow their lead on how much they want to talk, and make specific offers such as a ride to Thursday's appointment or a meal on Sunday. Keep in touch after treatment ends, when support often falls away. Avoid comparing their situation to someone else's, and avoid unsolicited advice about diets or alternative treatments.

Specific groups: young adults, pregnancy and older adults

Cancer is less common in young adults, which can make it harder to spot, because both patients and clinicians may not think of it. Colorectal cancer in people under 50 is a growing concern, and testicular cancer is most common in young men. If you are young and have a persistent symptom that does not have an explanation, it is reasonable to say so and ask whether further tests are needed. Young adults facing treatment should ask about fertility preservation before treatment begins, because some options are only possible beforehand.

Pregnancy brings its own questions. Cervical screening continues to be important, and a breast lump that develops during pregnancy or breastfeeding still needs checking, even though most are benign. Cancer during pregnancy is uncommon, and when it occurs it is managed by expert teams that plan treatment around the pregnancy. If you are pregnant and notice a warning sign, report it to your obstetric care provider rather than assuming it is a normal pregnancy change, and ask how any tests needed can be done safely.

Older adults carry most of the cancer burden, because risk rises with age. At the same time, screening becomes a more individual decision after about 75, when the balance of benefit and harm depends on overall health and life expectancy. Older adults with cancer often benefit from an assessment that looks at their overall health, medicines and support at home, which helps tailor treatment. Age alone should not rule out effective treatment.

Myths, talking to your doctor and a yearly plan

Myths about cancer cause real harm, mostly by delaying care or diverting people to treatments that do not work. Supplements do not reduce cancer risk in people who eat a reasonable diet, and beta-carotene supplements are linked to higher lung cancer risk in people who smoke. Cancer is not caused by deodorants, and cell phones have not been shown to cause cancer. Sugar does not feed cancer in a way that makes cutting it out a treatment. Alternative therapies used instead of standard treatment are linked to worse outcomes, so if you are interested in complementary approaches such as acupuncture or massage, use them alongside your treatment and tell your team.

At your yearly checkup, ask which cancer screenings are due for your age, sex and history, whether your family history changes anything, and whether you are up to date on the HPV and hepatitis B vaccines. If you smoke, ask for help quitting; medicines and counseling together give you a much better chance of success than willpower alone. If you have a symptom, describe it clearly and ask what the plan is if it does not go away.

A simple yearly routine makes it easier to keep on track. Treat it as a checklist rather than a source of worry; most of it takes very little time. The habits below cover the three things that make the biggest difference to most people: lowering risk where you can, getting the screenings that are due for your age, and acting quickly on symptoms that persist. Put the screening reminders in your calendar so they do not depend on memory.

• Once a year: review screenings due with your doctor, and complete any home stool test promptly
• Once a year: update your family health history and tell your doctor about new diagnoses in relatives
• Every month or so: notice how your skin and breasts or testicles normally look and feel, so change stands out
• Every day: no tobacco, less alcohol, more movement and sun protection when the UV index is high
• Any time: report a symptom that persists, changes or has no explanation, whatever your last screening showed

Every guide in this topic

• Warning Signs: What Published Guidance Supports
• Cancer Screening: What Published Guidance Supports
• Reducing Cancer Risk: Sorting the Evidence From the Noise
• Skin Cancer: What Published Guidance Supports
• Colorectal Cancer: Sorting the Evidence From the Noise
• Breast Cancer: Sorting the Evidence From the Noise
• What the Guidance Really Says About Cancer Survivorship
• Cancer and Family History: What Published Guidance Supports
• The Evidence on Cancer Treatment Side Effects, Without the Hype
• Talking About Cancer: What Published Guidance Supports

Frequently asked questions

At what age should I start colorectal cancer screening?

The USPSTF recommends that adults at average risk start at 45 and continue to 75. You may need to start earlier if a parent, sibling or child had colorectal cancer or advanced polyps, if you have inflammatory bowel disease, or if you have an inherited syndrome such as Lynch syndrome. Ask your doctor which test suits you; a yearly home stool test and a colonoscopy every 10 years are both good options.

Is a home stool test as good as a colonoscopy?

Both are recommended screening options. A colonoscopy looks directly at the colon and can remove polyps during the same procedure, but it needs bowel preparation and sedation. A home stool test is simple and private but must be repeated regularly, and any positive result needs a follow-up colonoscopy. The most effective test is the one you will actually complete on schedule.

I had a normal mammogram last year. Should I still get a new lump checked?

Yes. Screening looks for cancer in people without symptoms, and no mammogram catches every cancer. A new lump, skin change, nipple change or persistent pain needs checking whatever your last result showed. Most breast changes turn out to be benign, such as cysts, but the only way to know is a proper assessment, which may include a diagnostic mammogram or ultrasound.

Does cancer run in families?

Sometimes, but most cancers are not inherited. Because cancer is common, many families have several cases by chance. A pattern is more concerning when close relatives on the same side had the same or related cancers, were diagnosed young, or had more than one cancer. If that sounds like your family, ask your doctor about genetic counseling, which can clarify your risk and screening needs.

Can I lower my cancer risk if I have smoked for years?

Yes. Quitting lowers your risk of cancer and many other diseases at any age, and the benefit grows over time. Medicines and counseling together greatly improve your chances of quitting, and support is free through 1-800-QUIT-NOW. If you are 50 to 80 with a 20 pack-year history and smoke now or quit within 15 years, ask about yearly lung cancer screening.

Is the HPV vaccine worth getting as an adult?

Catch-up vaccination is recommended for everyone through age 26 who was not fully vaccinated. For adults aged 27 to 45, the vaccine is not routinely recommended, because many have already been exposed to HPV, but some may still benefit; it is a decision to make with your doctor. Vaccination does not replace cervical screening, which should continue as recommended.

Do supplements or special diets prevent cancer?

For most people, no. Large trials of vitamin and mineral supplements have generally not shown that they prevent cancer, and beta-carotene supplements are linked to higher lung cancer risk in people who smoke. An overall eating pattern rich in vegetables, fruit, whole grains and beans, with less processed meat and alcohol, is linked to lower risk. Talk to your doctor before starting any supplement.

What should I do if I get a fever during chemotherapy?

Call your cancer care team right away if your temperature is 100.4°F (38°C) or higher, or if you feel generally unwell, using their 24-hour number. Chemotherapy can lower the white cells that fight infection, and infection can become serious within hours. Go to the emergency room if you cannot reach them, and tell staff you are having chemotherapy.

How can I support a friend who has just been diagnosed?

Reach out, even if you are not sure what to say; silence is often felt more than clumsy words. Listen more than you talk, and let them decide how much to share. Make specific offers, such as driving them to an appointment or bringing a meal on a set day, rather than a general offer. Keep in touch over months, including after treatment ends.

Will my insurance pay for cancer screening?

Most private plans must cover USPSTF-recommended screenings with an A or B grade without a copay or deductible when you use an in-network provider, and Medicare covers the main cancer screenings. Costs can arise for follow-up tests or if a screening becomes diagnostic, so check with your insurer beforehand. If you are uninsured, ask about free breast and cervical screening programs in your state.

When to speak to a doctor

See your doctor promptly for unexplained weight loss, any new lump, a cough or hoarseness that does not go away, coughing up blood, blood in urine or stool, a lasting change in bowel or bladder habits, a changing mole, a sore that does not heal, difficulty swallowing, or bleeding after menopause, even if a recent screening test was normal. During or shortly after chemotherapy, call your cancer care team right away for a temperature of 100.4°F (38°C) or higher, and go to the emergency room if you cannot reach them. Call 911 for coughing up or vomiting large amounts of blood, severe chest pain, trouble breathing, confusion or collapse. If you or someone with cancer is thinking about suicide, call or text the 988 Suicide & Crisis Lifeline at 988.

Where this comes from

• American Cancer Society — Cancer Facts & Figures
• National Cancer Institute — Cancer Prevention Overview (PDQ)
• US Preventive Services Task Force — Colorectal Cancer: Screening
• US Preventive Services Task Force — Breast Cancer: Screening
• US Preventive Services Task Force — Cervical Cancer: Screening
• US Preventive Services Task Force — Lung Cancer: Screening
• US Preventive Services Task Force — Prostate Cancer: Screening
• CDC — HPV Vaccination
• National Cancer Institute — Side Effects of Cancer Treatment
• American Cancer Society — Guideline for Diet and Physical Activity for Cancer Prevention

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.