Cancer touches nearly every family in some way, and it comes with a lot of myths alongside the facts. The questions below are the ones people ask most often about cancer in general — not about any single type of the disease. Answers are based on current, publicly available guidance from major cancer organizations and are meant as a starting point for conversation with a qualified healthcare provider, not a substitute for one.
What exactly is cancer?
Cancer isn’t a single illness — it’s an umbrella term for more than a hundred related diseases that can start in almost any organ or tissue. What they share is a breakdown in the normal rules that govern how cells grow. Healthy cells divide, do their job, and eventually die off on a schedule controlled by our genes. Cancer begins when changes in a cell’s DNA cause it to ignore those signals: it keeps dividing when it shouldn’t, and it stops dying when it should. Over time, that runaway growth can form a mass, or tumor, and in some cases spread to other parts of the body.
What causes cancer?
At the cellular level, cancer is caused by changes to DNA that disrupt the normal instructions for cell growth and division. Some of these changes are inherited from a parent. Far more often, they build up over a lifetime because of things like tobacco use, excess UV exposure from the sun or tanning beds, certain infections, or simply the natural wear and tear of aging, since our cells become less efficient at repairing DNA damage as we get older.
No single event causes most cancers. It’s usually an accumulation of genetic changes over years or decades, which is one reason cancer becomes more common with age.
What is a “risk factor,” and does having one mean I’ll get cancer?
A risk factor is anything shown to raise the odds of developing a particular cancer — it is not a guarantee. Some risk factors, such as age or an inherited gene change, can’t be modified. Others, including tobacco use, alcohol consumption, excess body weight, physical inactivity, and prolonged sun exposure, can be reduced or avoided. Having one or more risk factors doesn’t mean a person will develop cancer, and plenty of people who develop cancer have few or no known risk factors. Risk factors describe probability across large groups of people, not a certainty for any one individual.
What’s the difference between a benign and a malignant tumor?
A tumor is simply a lump formed by a cluster of cells that have grown more than they should. A benign tumor stays in one place, doesn’t invade nearby tissue, and doesn’t spread elsewhere in the body — it isn’t cancer. A malignant tumor, by contrast, can grow into surrounding tissue and can send cells into the bloodstream or lymphatic system to form new tumors elsewhere. That capacity to invade and spread is what defines cancer.
What does it mean when cancer has “metastasized”?
Metastasis is the process by which cancer cells break away from the original, or primary, tumor and travel through the blood or lymphatic system to establish new tumors in other parts of the body. A metastatic tumor is still made up of cells from the original cancer, so, for example, breast cancer that spreads to the lungs is called metastatic breast cancer, not lung cancer. Doctors confirm this by examining the cells under a microscope, as the cells in the new location resemble those from where the cancer began. Widespread metastasis is the leading cause of death from cancer, which is a major reason early detection matters.
Is cancer contagious? Can I catch it from someone else?
No. Cancer cannot be transmitted from person to person the way a cold or the flu can. Living with, caring for, hugging, or sharing a meal with someone who has cancer will not put you at risk. The one indirect exception is that a small number of cancers are linked to infections — such as certain strains of HPV or hepatitis B and C — that are themselves contagious. In those cases, it’s the infection that can spread between people, not the cancer itself, and most people who get these infections never go on to develop cancer.
Because this is one of the most common misconceptions about cancer, it’s worth repeating: people going through cancer treatment need visits, closeness, and support, not distance.
Is cancer inherited? Does it run in families?
Sometimes, yes — but not usually in the way people assume. Only a modest share of cancers, generally estimated at around 5 to 10 percent, are linked to an inherited gene change passed down from a parent. What’s inherited is an abnormal gene that raises risk, not the cancer itself; a person who inherits such a gene has a higher chance of developing cancer but is not guaranteed to.
More often, cancer that seems to “run in a family” reflects shared habits or exposures — such as smoking, diet, or environment — or shared risk factors like excess body weight, rather than a single inherited gene. Anyone with a strong family history of cancer, especially at a young age or across multiple close relatives, may want to talk with a doctor or genetic counselor about whether genetic testing makes sense for them.
“Familial” and “hereditary” are not the same thing
These two words are often used interchangeably, but they describe different situations, and the distinction matters for how a family approaches screening and risk. Hereditary cancer means a specific, identifiable gene mutation has been passed from parent to child and can be confirmed with a genetic test. Familial cancer describes cases where several relatives develop the same cancer, but no single causative gene mutation has been found — the pattern is instead thought to reflect a combination of shared genetics, shared environment, and shared lifestyle habits.
Colorectal cancer is a well-studied example of how this plays out in practice, particularly in cases diagnosed at a younger-than-typical age. Two inherited syndromes account for a meaningful share of these early-onset cases:
Lynch syndrome is the most common inherited cause of colorectal cancer. It results from mutations in genes responsible for DNA mismatch repair, the cellular system that normally corrects copying errors in DNA. People with Lynch syndrome face a substantially higher lifetime risk of colorectal cancer and also of several other cancers, including endometrial cancer.
Familial adenomatous polyposis (FAP) is caused by mutations in the APC gene. It leads to the development of hundreds to thousands of precancerous polyps in the colon and rectum, often beginning as early as the teenage years. Left untreated, these polyps are extremely likely to eventually become cancerous, which is why FAP is typically managed with close surveillance and, often, preventive surgery.
Both are examples of true hereditary syndromes, confirmed through genetic testing, as opposed to “familial” clustering with no single identified mutation. The same basic distinction — a confirmed inherited gene change versus a family pattern without one — applies across many cancer types, not just colorectal cancer; it’s simply one of the best-documented examples.
Can stress cause cancer?
This is a widely studied question, and the honest answer is that there’s no clear, consistent evidence that psychological stress by itself increases a person’s risk of developing cancer. Stress does affect the immune system and overall health, but researchers have not established a direct causal link between stress levels and cancer occurrence. What stress can do is affect behaviors — sleep, eating, exercise, tobacco or alcohol use — that are themselves connected to cancer risk. Managing stress is worthwhile for overall wellbeing, but there’s no evidence that a person’s cancer occurred because of it.
Does a person’s attitude, personality, or emotional state affect whether they get cancer, or how it turns out?
No. Research has not found a connection between personality type, outlook, or emotional state and either the likelihood of developing cancer or the outcome of treatment. A cancer diagnosis is not something a person brought on themselves through their thinking or temperament, and staying positive, while it can support quality of life during treatment, does not change survival odds on its own. This is an important point for patients and families to hear, because guilt or self-blame around a diagnosis is common and unfounded.
Does sugar “feed” cancer?
This is one of the most persistent myths in oncology, and it isn’t supported by evidence. All cells in the body, cancerous and normal alike, use sugar (glucose) for energy, but eating sugar has not been shown to make existing cancer grow faster, spread, or worsen, nor does sugar intake on its own raise the risk of developing cancer. The real connection is indirect: diets high in sugar and sugar-sweetened beverages contribute to excess calorie intake and weight gain, and excess body weight is itself an established risk factor for several cancers. Cutting sugar for its own sake won’t “starve” a tumor, but maintaining a healthy weight through diet and activity is a genuinely useful part of cancer prevention.
Can an injury, like a bruise or a broken bone, cause cancer?
No. Falls, bumps, bruises, and broken bones do not cause cancer. Occasionally, a person seeks care for an injury and a cancer is discovered in the process, such as an X-ray for a fracture that happens to reveal something unrelated. In those cases, the injury didn’t cause the cancer, it simply led to the tumor being found sooner than it might have been otherwise.
Can cancer be prevented?
Not every cancer can be prevented, but a substantial share of cases are linked to modifiable factors, so real prevention is possible. The most consistently supported steps are: not using tobacco in any form and avoiding secondhand smoke; maintaining a healthy body weight; staying physically active; limiting alcohol; eating a diet rich in vegetables, fruit, and whole grains while limiting red and processed meat; protecting skin from excess UV exposure; and getting recommended vaccines, such as the HPV vaccine and hepatitis B vaccine, which protect against infections linked to certain cancers. Regular recommended screening also plays a preventive role for some cancers, because it can catch and remove precancerous changes before they ever become cancer.
What is cancer screening, and why does it matter?
Screening means testing for cancer, or for changes that could lead to cancer, in people who have no symptoms. The goal is to find disease at its earliest, most treatable stage, or in some cases to catch precancerous changes before they ever become cancer. Cancers found through screening tend to be smaller and less likely to have spread, which generally improves outcomes. Recommended screening tests, and the age at which to start them, differ by cancer type and by individual risk factors such as family history, so the right schedule is something to work out with a healthcare provider rather than a one-size-fits-all rule.
How is cancer diagnosed and staged?
Diagnosis typically starts with a doctor investigating a symptom, a screening result, or an incidental finding, using some combination of imaging (like CT, MRI, or PET scans), lab tests, and a biopsy, in which a small sample of tissue is examined under a microscope to confirm whether cancer cells are present. Once cancer is confirmed, it is usually assigned a stage, a standardized way of describing how large the tumor is and whether it has spread to lymph nodes or distant organs. Staging matters because it guides treatment decisions and helps predict prognosis; earlier-stage cancers are generally more treatable than cancers that have spread widely.
Is cancer becoming more common, or are we making progress against it?
Both things are true at once, in different ways. Globally, cancer remains one of the leading causes of death, and the World Health Organization has reported that it accounted for nearly 10 million deaths in a recent year, close to one in six deaths worldwide. At the same time, in the United States, the overall cancer death rate has been declining for years, thanks largely to reductions in smoking, earlier detection through screening, and steady advances in treatment. As death rates have fallen, the number of people living as cancer survivors has grown substantially. Progress is real, even though the overall global burden remains significant, partly because the world’s population is older and larger than it used to be.
Can cancer be cured?
Many cancers can be cured, especially when found early, and doctors often describe long-term remission or “no evidence of disease” rather than using the word “cured,” since some cancers can recur years later. Outcomes vary enormously depending on the type of cancer, its stage at diagnosis, and the treatment options available, so it isn’t possible to give one answer that applies to all cancers. What is broadly true is that survival rates for most cancers have improved over recent decades as screening, surgical techniques, radiation, chemotherapy, targeted therapy, and immunotherapy have all advanced.
A note on this information: This FAQ is provided for general education and does not replace advice from a qualified healthcare professional. If you or someone you love has questions about a specific diagnosis, risk, or symptom, please talk with a doctor. In the United States, the National Cancer Institute’s information specialists can be reached at 1-800-4-CANCER, and the American Cancer Society’s helpline is available 24/7 at 1-800-227-2345.
Sources consulted:
- National Cancer Institute (NCI), cancer.gov — “What Is Cancer?”, “Cancer Causes and Prevention,” “Cancer Statistics,” and PDQ® cancer information summaries
- American Cancer Society, cancer.org — “Common Questions About Causes of Cancer” and ACS cancer screening guidelines
- World Health Organization — Cancer fact sheet
- MedlinePlus (U.S. National Library of Medicine) — “Cancer”
