What Is Cancer? Understanding the Causes, Types, Symptoms and How Cancer Develops
mark ogujiuba What Is Cancer? Understanding the Causes, Types, Symptoms and How Cancer Develops
The word cancer can be frightening. It's a word most people have heard, but many people still wonder what cancer actually is, how it starts, what causes it, and whether it can be prevented.
Cancer isn't a single disease. It's a large group of diseases that can develop in almost any part of the body.
At its simplest, cancer occurs when some of the body's cells begin to grow and divide in an uncontrolled way. You know what? These abnormal cells may invade nearby tissues and, in some cases, spread to other parts of the body. (National Cancer Institute)
According to the world health organization (who), cancer was responsible for nearly 10 million deaths worldwide in 2024The truth is, making it one of the world's leading causes of death. At the same time, many cancers can be prevented, detected early, or successfully treated. (World Health Organization)
So, what exactly happens when normal cells become cancerous?
Let's start from the beginning.
What Is Cancer?
Cancer is a disease in which abnormal cells grow uncontrollably and may invade surrounding tissues or spread to other parts of the body.
Your body is made up of trillions of cells. Normally, these cells follow an organized process:
Cells grow when they need it.
Cells are divide to produce new cells.
Damaged or old cells are removed.
New healthy cells replace them.
This process is tightly controlled by genes inside our cells.
Cancer develops when changes occur in these genes and disrupts the normal controls over cell growth, division, and survival. (National Cancer Institute)
This means that cancer is fundamentally a disease involving abnormal changes in cells and the genes that control them.
How Does Cancer Develop?
To understand cancer, it helps to understand what happens inside a normal cell.
Think of your genes as a set of instructions that tell your cells what to do.
Some genes tell cells when to grow and divide. Others tell them when to stop dividing, repair damaged DNA, or die when they're no longer needed.
Cancer can develop when changes occur in genes that control these processes.
These changes can allow abnormal cells to:
Grow when they shouldn't
Continue dividing when they should stop
Avoid normal cell death
Accumulate additional genetic changes
Invade nearby tissues
Spread to other parts of the body
The National Cancer Institute explains that cancer-causing genetic changes can occur because of random errors during cell division, DNA damage caused by environmental exposures, or inherited genetic changes. (National Cancer Institute)
Cancer usually does not appear because of one single event.
In many cases, several genetic changes accumulate over time.
What Causes Cancer?
There's usually no single answer to the question, "What caused this person's cancer?"
Cancer can result from a combination of genetic, environmental, and lifestyle-related factors.
Some risk factors can be changed, while others can't.
The WHO groups on important cancer-causing influences into several broad categories, including physical, chemical and biological carcinogens. (World Health Organization)
Let's look at some of them.
1. Tobacco
Tobacco use is one of the best-established preventable causes of cancer.
Smoking exposes the body to numerous chemicals that can damage DNA and contribute to cancer development.
Tobacco is associated with several cancers, including cancers of the:
Lung
Mouth
Throat
Esophagus
Bladder
Kidney
Liver
Pancreas
Stomach
Colon and rectum
WHO identifies tobacco use as one of the major preventable cancer risk factors. (World Health Organization)
2. Alcohol
Alcohol consumption is also associated with cancer risk.
Alcohol has been linked to several types of cancer, including cancers of the mouth, throat, esophagus, liver, breast, and colon and rectum. (World Health Organization)
Cancer risk can be influenced by the amount and pattern of alcohol consumption.
The important message is that alcohol isn't simply a lifestyle choice unrelated to health; it can contribute to disease risk.
3. Ultraviolet Radiation
Ultraviolet (UV) radiation from the sun can damage DNA in skin cells.
Repeated or excessive exposure to UV radiation can increase the risk of skin cancer.
This is why protecting your skin from excessive UV exposure is an important part of cancer prevention.
4. Certain Infections
Some infections can increase the risk of developing certain cancers.
Examples include:
Human papillomavirus (HPV)
Hepatitis B virus
Hepatitis C virus
Helicobacter pylori
Epstein-Barr virus
According to WHO, cancer-causing infections account for a significant proportion of cancers in low- and lower-middle-income countries. (World Health Organization)
This is one reason vaccination, infection prevention and appropriate medical treatment can play a role in cancer prevention.
5. Environmental and Occupational Exposures
People can sometimes be exposed to substances that increase cancer risk through their environment, workplace, or everyday activities.
Examples include certain chemicals, asbestos, air pollution, and other carcinogenic substances.
The risk depends on the substance, the level of exposure, how often exposure occurs, and how long it continues.
For example, radon exposure is an established cause of lung cancer.
MedsLearn has explored some potentially harmful household exposures in 10 Cancer-Causing Things Hiding in Your Home (+ Safe Swaps). The article also emphasizes an important point: exposure to something potentially harmful does not mean that cancer is inevitable. Risk depends on factors such as the substance and the level and duration of exposure.
6. Diet, Physical Activity and Body Weight
Lifestyle factors can also influence cancer risk.
WHO identifies tobacco use, alcohol consumption, unhealthy diet, physical inactivity, and high body mass index among important cancer risk factors. (World Health Organization)
But this does not mean that eating one food will prevent cancer or that one unhealthy meal will cause it.
Cancer development is much more complicated than that.
Instead, think about your overall lifestyle over time.
For practical guidance on caring for your body through exercise, nutrition, sleep and other everyday habits, see MedsLearn's Physical Health: Caring For Your Body.
Can Cancer Be Inherited?
This is an important question because cancer sometimes appears to "run in families."
But there's a difference between inheriting a genetic change that increases cancer risk and inheriting cancer itself.
Cancer itself isn't passed directly from parent to child.
Though some people inherit genetic changes that increase their likelihood of developing particular cancers.
For example, inherited changes in genes such as BRCA1 and BRCA2 can increase the risk of several cancers. (National Cancer Institute)
By the way, the national cancer institute estimates that inherited genetic changes account for a minority of cancers. Most cancer-causing genetic changes arise during a person's lifetime rather than being inherited. (National Cancer Institute)
What's interesting is so having a family member with cancer does not mean you'll definitely develop cancer.
It does, however, make your family history worth discussing with a healthcare professional.
Why Does Cancer Become More Common with Age?
Cancer can occur at different ages, including children and young adults.
Yet, the overall risk of cancer increases substantially with age.
One reason is that genetic changes can accumulate over many years. At the same time, the body's ability to repair certain types of cellular damage can become less effective with age. (National Cancer Institute)
This does not mean that getting older means you'll develop cancer.
It means that age is one of several factors that influence cancer risk.
What Is the Difference Between a Tumor and Cancer?
The truth is, these terms are sometimes used interchangeably, but they aren't exactly the same.
A tumor is an abnormal mass of tissue that develops when cells grow or divide more than they should, or when they fail to die when they should.
Tumors can be:
Benign
A benign tumor is not cancer.
You know what? Benign tumors generally don't invade nearby tissues or spread to distant parts of the body. But some benign tumors can still cause serious health problems depending on their location and size. (National Cancer Institute)
Malignant
A malignant tumor is cancerous.
Malignant cancer cells can invade nearby tissues and may spread to other parts of the body.
Importantly, not all cancers form solid tumors.
For example, leukemia is a cancer of blood-forming tissues and generally does not produce a solid tumor. (National Cancer Institute)
What Are the Main Types of Cancer?
There are more than 100 types of cancer.
Here's what I found they're commonly named according to where they begin or the type of cell from which they develop. (National Cancer Institute)
Some major categories include:
Carcinomas
Carcinomas begin in epithelial cells, which cover the body's surfaces and line many organs.
Examples include:
Breast cancer
Lung cancer
Prostate cancer
Colorectal cancer
Skin cancers
Many common cancers are carcinomas.
Sarcomas
Sarcomas develop in connective or supportive tissues such as:
Bone
Muscle
Fat
Cartilage
Blood vessels
they're less common than carcinomas.
Leukemias
Leukemias are cancers of blood-forming tissues, particularly bone marrow.
Unlike many solid cancers, leukemia generally does not form a solid tumor. Instead, abnormal blood-forming cells accumulate in the blood and bone marrow. (National Cancer Institute)
Lymphomas
Lymphomas are cancers that begin in lymphocytes, a type of white blood cell that forms part of the immune system.
They can develop lymph nodes and other tissues.
Other Cancers
There are also cancers such as:
Multiple myeloma
Melanoma
Brain and spinal cord cancers
Germ cell tumors
Neuroendocrine tumors
Each type of cancer can behave differently and may require different approaches to diagnosis and treatment.
What Are the Symptoms of Cancer?
there's no single symptom that means someone has cancer.
Cancer can produce many different symptoms depending on:
The type of cancer
Where it begins
Its size
Whether it has spread
Which organs or tissues are affected
Some cancers cause noticeable symptoms early, while others may cause few or no symptoms until they become more advanced. (National Cancer Institute)
Possible warning signs can include:
An unexplained lump or swelling
Unexplained weight loss
Persistent or unexplained fatigue
Changes in bowel habits
Changes in bladder habits
Persistent cough or difficulty breathing
Unexplained bleeding
Persistent pain
Changes in the skin, such as a changing mole
Difficulty swallowing
Persistent fever or night sweats in some circumstances
But there's an important point here:
Most of these symptoms can be caused by conditions other than cancer.
For example, a lump may be benign, fatigue can have many causes, and changes in bowel habits can result from infections or digestive conditions.
The National Cancer Institute recommends speaking with a healthcare professional about symptoms that persist rather than if they're cancer or ignoring them because they aren't painful. (National Cancer Institute)
Does Cancer Always Cause Pain?
No.
Cancer does not always cause pain, especially during its early stages.
This is why waiting until something hurts before seeking medical attention isn't a good general strategy.
Some cancers can develop without producing noticeable symptoms for a considerable period.
If you notice a persistent or unusual change in your health, it's better to discuss it with a healthcare professional rather than trying to determine its cause yourself. (National Cancer Institute)
How Is Cancer Diagnosed?
Doctors use different tests to investigate whether cancer may be present.
The exact process depends on the symptoms and suspected type of cancer.
Tests may include:
Medical history and physical examination
A healthcare professional will ask about symptoms, medical history, family history, and other relevant factors.
A physical examination may also be performed.
Laboratory tests
Blood, urine, or other laboratory tests may sometimes provide information that helps doctors investigate possible cancer.
But laboratory abnormalities don't automatically mean someone has cancer.
Imaging
Depending on the situation, doctors may use imaging tests such as:
X-rays
Ultrasound
CT scans
MRI
PET scans
Biopsy
A biopsy involves removing a sample of tissue so that it can be examined under a microscope.
For many cancers, a biopsy is an important part of confirming a diagnosis.
The exact diagnostic process varies significantly between cancer types.
What Does "Cancer Stage" Mean?
By the way, if someone is diagnosed with cancer, doctors may determine their stage.
Cancer staging describes how extensive cancer is.
Depending on the type of cancer, staging may consider factors such as:
The size of the tumor
Whether nearby lymph nodes are involved
Whether the cancer has spread to other parts of the body
A cancer that has spread from its original location to another part of the body is described as metastatic cancer. (National Cancer Institute)
For example, if breast cancer spreads to the lungs, it remains metastatic breast cancer; it does not become lung cancer.
Knowing the stage helps healthcare professionals understand the disease and plan appropriate treatment.
What Is Metastasis?
Metastasis is the process through which cancer cells spread from where they originally developed to another part of the body.
Cancer cells can travel through the bloodstream or lymphatic system and establish themselves in other tissues.
Metastatic cancer retains the identity of the original cancer.
For example:
Prostate cancer that spreads to the bones is still prostate cancer, not bone cancer.
Metastatic disease can be more difficult to treat, which is one reason early detection and appropriate treatment are important for cancers where effective screening or early diagnosis is possible. (National Cancer Institute)
Can Cancer Be Prevented?
Not every cancer can be prevented.
Some risk factors can't be changed, including:
Age
Certain inherited genetic changes
Family history
But a substantial proportion of cancers are associated with preventable or modifiable risk factors.
The WHO estimates that approximately 38% of cancers can currently be prevented through avoiding risk factors and implementing evidence-based prevention strategies. (World Health Organization)
Cancer prevention can include:
Avoiding tobacco
Limiting alcohol consumption
Maintaining a healthy body weight
Being physically active
Eating a healthy diet
Protecting the skin from excessive UV exposure
Reducing exposure to known carcinogens
Getting recommended vaccinations, such as HPV and hepatitis B vaccination where appropriate
Managing certain infections
Participating in recommended cancer screening
MedsLearn's Preventive Health: Definition, Importance, and Ways to Prevent Disease explores the broader idea of preventing illness before it becomes a serious health problem.
Does Getting Cancer Mean Someone Did Something Wrong?
No.
This is an important message that's sometimes overlooked.
Cancer is complicated.
A person can live a healthy lifestyle and still develop cancer. Someone may develop cancer because of inherited genetic factors, random cellular changes, environmental exposures, infections, or a combination of several factors.
Cancer shouldn't automatically be viewed as the result of a person's choice or character.
Understanding risk factors is useful because it can help people make healthier decisions, but risk isn't the same as certainty.
Is Cancer Contagious?
In general, cancer itself isn't contagious.
You can't catch cancer from another person through ordinary contact such as:
Hugging
Touching
Sharing food
Sitting beside someone
Caring for someone with cancer
But, some infections that can increase cancer risk can spread between people.
For example, HPV and hepatitis B can be transmitted between people, and chronic infection with these viruses can increase the risk of certain cancers. (World Health Organization)
This is an important distinction between an infection and the cancer that may develop later as a consequence of that infection.
Can Cancer Be Cured?
Some cancers can be cured, particularly when they're detected early and treated effectively.
Still, the word "cure" can't be applied in exactly the same way to every cancer.
Treatment and outcomes depend on factors such as:
Cancer type
Stage
Grade
Location
Genetic characteristics
Overall health
Response to treatment
Modern cancer treatment can include surgery, radiation therapy, chemotherapy, immunotherapy, targeted therapy, hormone therapy and other approaches.
Doctors may use one treatment or combine several approaches depending on the specific cancer.
WHO notes that many cancers can be cured when they're detected early and treated appropriately. (World Health Organization)
What Should You Do If You're Worried About Cancer?
Don't panic, and don't try to diagnose yourself from something you read online.
If you notice a persistent or unusual change in your health, speak with a qualified healthcare professional.
Depending on your age, sex, family history and other risk factors, your healthcare professional may also recommend specific screening tests.
Screening is different from diagnosis.
Screening looks for disease before symptoms appear, while diagnostic testing investigates a problem that may already be present.
Not every cancer has an effective screening test, and not everyone needs every screening test.
Your healthcare professional can help you understand what is appropriate for you.
Cancer and the Importance of Early Detection
One of the most important ideas in cancer care is early detection.
When certain cancers are found before they have spread, treatment may be more effective, and the chances of successful treatment can be higher.
But early detection does not mean every cancer should be screened for every person.
Different cancers have different screening recommendations, and screening can have both benefits and harms.
The right approach depends on the cancer, the person's age, risk factors, and applicable clinical guidelines.
Cancer isn't the End of the Story
A cancer diagnosis can be frightening, but a diagnosis isn't automatically a death sentence.
Cancer treatment has changed dramatically over the years, and researchers continue to develop new ways to detect, prevent and treat cancer.
Some cancers can be cured. Others can be controlled for long periods. For some people, treatment focuses on slowing the disease, relieving symptoms and maintaining quality of life.
What matters is getting accurate information and appropriate medical care rather than relying on fear, myths or unproven treatments.
What You Should Remember About Cancer
Cancer is complicated, but the basic idea can be understood.
Remember these key points:
Cancer isn't a disease. It's a large group of related diseases.
Cancer develops when cells acquire changes that disrupt normal growth and survival controls.
Cancer can occur in almost any part of the body.
Some genetic changes are inherited, while others develop during a person's lifetime.
Age, family history, lifestyle, environmental exposures and certain infections can influence cancer risk.
Cancer is not contagious.
A tumor isn't automatically cancer; some tumors are benign.
Cancer symptoms vary depending on the type and location of the disease.
Many symptoms associated with cancer can also be caused by non-cancerous conditions.
Persistent or unusual symptoms should be evaluated by a healthcare professional.
Some cancer can be prevented.
Some cancers can be detected early through appropriate screening.
Many cancers can be successfully treated, especially when detected early.
Having a risk factor does not mean that you'll definitely develop cancer.
Frequently Asked Questions About Cancer
What is cancer in simple words?
Cancer is a group of diseases in which abnormal cells grow and divide without normal control. These cells can sometimes invade nearby tissues or spread to other parts of the body. (National Cancer Institute)
What causes cancer?
Cancer can result from genetic changes that develop during a person's lifetime, inherited genetic changes, environmental exposures, certain infections, and other factors. Often, several factors contribute, and the exact cause of an individual person's cancer may never be known. (National Cancer Institute)
Is cancer hereditary?
Some cancer-risk genetic changes can be inherited, but cancer itself isn't simply passed from parent to child. Only a minority of cancers are caused primarily by inherited genetic changes. (National Cancer Institute)
Is cancer contagious?
No. Cancer itself isn't contagious. Still, some infections that can increase cancer risk, such as HPV and hepatitis B, can spread between people. (World Health Organization)
What are the warning signs of cancer?
Possible signs include unexplained lumps, persistent changes in bowel or bladder habits, unexplained bleeding, persistent cough, unexplained weight loss, persistent pain, and certain skin changes. Though these symptoms have many possible causes and don't automatically mean cancer. (National Cancer Institute)
Can cancer be prevented?
Some cancers can be prevented by reducing exposure to known risk factors and using evidence-based prevention strategies. Yet not every cancer can be prevented. (World Health Organization)
Can cancer be cured?
Some cancers can be cured, particularly when detected early and treated effectively. Outcomes vary considerably depending on the type and stage of cancer. (World Health Organization)
Does having a lump mean I have cancer?
No. Many lumps are caused by non-cancerous conditions. Yet, a new, persistent, or unexplained lump should be assessed by a healthcare professional rather than self-diagnosed.
Final Word
Cancer is a complicated group of diseases, but understanding the basics can make it less mysterious and less frightening.
Cancer develops when changes in cells disrupt the normal systems that control growth, division and cell death. These changes can arise through a combination of inherited genetics, aging, environmental exposures, infections, and other factors.
You can't control every cancer risk.
But you can make informed choices about the risks you can control, pay attention to persistent changes in your health, follow appropriate prevention measures and speak with a healthcare professional when something doesn't seem right.
Knowledge does not eliminate cancer, but it can help us recognize risk, seek care earlier, and make better decisions about our health.
Medical Disclaimer
This article is intended for general health education and does not replace medical diagnosis, treatment or personalized advice from a qualified healthcare professional. Cancer symptoms, screening recommendations, treatment options, and individual risks vary. If you have concerns about your health or symptoms that persist, speak with a qualified healthcare professional.
