What Is Cancer?

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Types of Cancer
- Carcinoma The most common type, this forms in the cells that line the surfaces of organs, known as epithelial cells. Subtypes include adenocarcinomas, basal cell carcinomas, squamous cell carcinomas, and transitional cell carcinomas.
- Sarcoma These form in bone and in soft tissues such as muscles, fat, blood vessels, and lymph vessels. The most common bone cancer is osteosarcoma.
- Leukemia Leukemias are cancers that begin in blood-forming cells in the blood and bone marrow. They typically do not form solid tumors but instead cause white blood cell buildup that crowds out normal blood cells. This can affect your body’s ability to protect you from infections, control bleeding, or get enough oxygen to tissues.
- Lymphoma Lymphomas develop from white blood cells, known as lymphocytes. Healthy lymphocytes play an important role in your immune system, helping you recover from infections and supporting wound healing.
- Melanomas These develop from the cells that become melanocytes — the cells responsible for the pigment that provides skin color, melanin. Most melanomas are skin cancers, but some can grow in other tissues that contain melanin, such as the eye.
- Multiple Myeloma Also known as plasma cell myeloma, this is another type of cancer of blood cells that forms in a type of immune cell called a plasma cell. Abnormal plasma cell buildup in bone marrow can form tumors throughout the body.
- Brain and Spinal Cord Tumors Different types of tumors can form in the brain and nervous system. These are named after the types of nervous system cells in which they start.
- Neuroendocrine and Carcinoid Tumors These affect cells that respond to nerve signals by releasing hormones. Rarely, neuroendocrine tumors (NETs) can lead to raised hormone levels and cause a range of symptoms, and they can be either benign (not cancerous) or malignant. Doctors classify these by whether they release hormones (functional NETs) or don’t (non-functional NETs). However, both types can cause symptoms. They also classify NETs by where they grow.
- Germ Cell Tumors These tumors begin in cells that go on to become sperm or eggs. However, they aren’t limited to your reproductive organs, can develop almost anywhere, and may also be either benign or malignant.
Signs and Symptoms of Cancer
- Extreme tiredness
- Unexpected weight loss
- Coughing up blood
- Difficulty swallowing
- Muscle or joint pain you can’t explain, with progressive pain
- Fevers or night sweats you can’t explain
- Bleeding or bruising you can’t explain
- Blood in your urine or stool
- Changes in how often you pass urine or stool
- A hoarse voice
- New lumps
- Skin changes, including changes to existing moles, color changes in areas of skin, including darkening, redness, or yellowing, or sores that don’t get better
See your doctor about any ongoing symptoms that are causing concern or if you have new symptoms that last for over two weeks.
Causes and Risk Factors of Cancer
- Some mutations cause cells to copy themselves faster.
- Other changes prevent cells from knowing when to stop dividing.
- Many mutations keep cells from dying at the natural point in their life cycle.
- UV radiation from the sun or tanning beds
- Exposure to hazardous chemicals, known as carcinogens, in your environment, such as benzene, asbestos, or radon
- Certain viruses, like some types of human papillomavirus (HPV) or hepatitis B
- Lifestyle choices, such as smoking, not wearing sun protection when outside, or HIV infection
- Uncontrollable factors like your age, ethnic background, and sex
- Other health problems, like ulcerative colitis
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How Is Cancer Diagnosed?
Some cancers can begin to grow without any signs or symptoms. To find those cancers early, researchers have developed a variety of screening tools to detect them before they become apparent.
Screening and diagnosis are different. A positive result in a screening test does not mean you have cancer. But it often means that you need more tests to make a diagnosis.
Screening Tests
- Breast Cancer Screening Healthcare professionals can carry out a scan called a mammography (mammogram) to detect breast cancer early. Expert groups generally recommend screening for women starting at age 40 and continuing through age 74.
- Colorectal Cancer Screening Screenings for colorectal cancer involve procedures like a colonoscopy or sigmoidoscopy, in which a doctor inserts a flexible, lighted tube with a camera attached to look for and sometimes remove unusual tissue in the colon and rectum. Stool tests can also screen for colorectal cancer. Regular screening is recommended for people at average risk between the ages of 45 and 75.
- Cervical Cancer Screening Pap tests and HPV tests can show cell changes or detect HPV, a cancer-linked virus, before cervical cancer develops. Experts generally recommend starting cervical cancer screening at 21 to 25 years of age and ending at age 65.
- Lung Cancer Screening A type of CT scan called low-dose helical computed tomography is recommended for some current or former heavy smokers between the ages of 50 and 80 years.
- Alpha-fetoprotein (AFP) Blood Test This blood test, sometimes done in addition to a liver ultrasound, is used to detect liver cancer in high-risk individuals.
- Breast MRI This involves imaging for breast cancer in those with dense breast tissue or particular genetic mutations, such as BRCA.
- CA-125 Test A healthcare professional may give a blood test to check for ovarian cancer in high-risk or symptomatic women, often with an ultrasound.
- Breast Exams A medical professional may recommend an inspection of the breasts for signs of breast cancer if they’ve noticed unusual lumps or changes.
- PSA Test A prostate-specific antigen (PSA) blood test and digital rectal exam (DRE) can help a doctor check for prostate cancer in high-risk men.
- Skin Exams These involve visual inspection for skin cancer in at-risk individuals or in those noticing changes in moles.
- Transvaginal Ultrasound Imaging in people with BRCA mutations or Lynch syndrome can help identify early signs of ovarian or endometrial cancer.
- Virtual Colonoscopy If people decline invasive colonoscopies or sigmoidoscopy, a healthcare professional can perform an external CT scan to check for colorectal cancer.
Diagnostic Tests
- Imaging This is a common tool that can confirm suspicious findings from cancer screening, including CT scans, X-rays, and MRIs.
- Endoscopy A clinician may insert a tube with a lighted camera into the body to take a careful look around and possibly remove certain tumors.
- Biopsy A healthcare professional collects a sample of cells from the affected area and sends it for examination under a microscope. They might use either a needle (less invasive) or a scalpel to access the tumor. The cells are examined to check whether they are cancerous or benign.
- Tumor Marker Testing A blood sample can show raised levels of certain proteins or signs of tumors known as tumor markers.
Staging and Grading Cancer
- Stage 0: This often describes a precancer (abnormal cells with a risk of turning into cancer) or benign tumor.
- Stages 1-3: These usually involve cancers that haven’t moved from their original site. Those that have spread (often stage 2 or 3 cancers) may have moved into nearby tissue or lymph nodes.
- Stage 4: This is often the most advanced stage of a cancer, meaning it has spread to distant sites in the body, far from where it first developed.
Treatment and Medication Options for Cancer
Medication Options
Doctors specializing in treating cancers, or oncologists, can prescribe a huge variety of medications. These are designed to destroy cancers, prevent their growth, and deprive them of nutrients or blood. Others target parts of the cancer cell or help your immune system pinpoint the cancer so it can work against it.
- Chemotherapy This uses infusions, injections, creams, or oral medications to destroy cancer cells, but it can also damage noncancerous cells. This can lead to side effects, including anemia, hair loss, nausea, and vomiting.
- Immunotherapy This treatment uses medications that help your immune system spot and kill cancer cells. Cancer cells can hide from your immune system, but immunotherapy helps your body recognize and destroy cancer cells.
- Targeted Therapy Some cancer cells have certain mutations that make proteins that encourage cancer cell growth. Targeted therapy drugs block or disable these abnormal proteins. If your cancer cells have one of these specific mutations, a doctor may recommend this type of treatment.
- Hormone Therapy This treatment slows or stops the growth of cancer cells that use hormones to grow. Doctors recommend it primarily for hormone-sensitive cancers, most commonly breast and prostate cancers. Hormone therapy can help reduce the risk of some cancers returning after surgery.
Surgery
A surgeon might use open surgery, removing the tumor through a large cut, or minimally invasive surgery, operating through several small cuts using a laparoscope (a long tube with an attached camera or a robotic arm).
Ablation Therapy
- Cryosurgery or Cryotherapy This involves using liquid nitrogen or argon gas to apply extreme cold to abnormal tissue, which destroys it. It plays a role in the treatment of skin cancer, some cancers of the eye, and cervical cancer.
- Hyperthermia Although it’s not yet widely available, hyperthermia exposes small areas of tissue to extremely high temperatures that kill cancer cells or increase how much they respond to other treatments. Radiofrequency ablation is a type of hyperthermia that uses high-energy radio waves to create heat.
- Laser Surgery These are highly precise and use powerful, hot light beams to cut tissue. They can destroy tumors, shrink them, or remove benign tumors or precancers that may later become cancerous, often on the skin’s surface or the inside linings of organs. Cancer surgeons often use them to treat basal cell carcinoma, abnormal cells in the cervix, and cancers of the cervix, esophagus, vagina, and lungs.
Radiation Therapy
- External Beam Radiation Therapy The most common type, a radiation oncologist targets a tumor with a machine that produces a beam of high-energy radiation. Most often, the energy is X-rays, but they may also use electrons or protons.
- Internal Radiation Therapy This places the radioactive source inside the body, often to treat head, neck, cervix, breast, uterus, or prostate cancers. For brachytherapy, a radiation oncologist may place solid radioactive material, or a “seed,” next to the tumor. Systemic therapy uses a pill or intravenous injection of a radioactive protein that recognizes, attaches to, and releases radiation into specific cancer cells.
Bone Marrow Transplants
- Allogeneic This uses healthy stem cells from a donor with blood similar to yours –– often a close relative.
- Autologous This uses healthy stem cells from your own body.
Complementary and Integrative Therapies
- Acupuncture
- Hypnosis
- Massage therapy (possibly with modified technique)
- Mindfulness-based stress reduction
- Tai chi and Qigong
- Yoga
- Dietary supplements, such as ginger
Disparities and Inequities in Cancer
- More Black people die from many (but not all) cancers than people in other racial or ethnic groups.
- Black women have lower breast cancer rates than white women, but are more likely to die if they have it.
- People in rural Appalachia are more likely to have colorectal, cervical, or lung cancer than people in urban parts of the same region.
- Black men with prostate cancer have more than double the mortality risk of white men with prostate cancer.
- Regardless of ethnicity, people with a higher education level have a lower risk of dying from colorectal cancer before 65 years of age than those with less education.
- Black, Hispanic/Latino, Native American, and Alaska Native women have higher rates of cervical cancer than those in other racial and ethnic groups. Black women have the highest rate of death from cervical cancer.
- Native Americans and Alaska Natives have a higher risk of death from kidney cancer than any other ethnic or racial group. This group also has the highest rate of liver and intrahepatic bile duct cancer.
Lifestyle Changes and Prevention of Cancer
- Avoiding or quitting tobacco
- Eating a healthy diet
- Limiting alcohol consumption
- Managing body weight
- Exercising regularly
- Using sun protection
- Receiving Hepatitis B and HPV vaccinations
- Following cancer screening recommendations
Cancer Prognosis
- The type of cancer
- Which part of the body has cancer
- The cancer’s grade and stage
- Certain genes or hormone receptors in the cancer cells
- Your age
- Your overall health
- Which treatments you have and how your body responds to them
Cancer Complications
- Spinal Cord Compression Cancers on or near the spinal cord or its nerves can cause reduced function and pain. Sometimes this can cause issues with control of urination or bowel movements. The longer a tumor presses against the spinal cord, the less likely it is that treatment will restore normal function.
- Brain Function Issues Brain cancers can alter how your brain works. Symptoms vary but might include confusion, agitation, headaches, weakness, seizures, nausea, vomiting, and changes in how you see or feel things.
- Hypercalcemia Cancer cells may cause abnormally high calcium levels in the blood, and this is the most common life-threatening complication of cancer in adults.
- Blood Clots Cancer can make the blood thicker and stickier, making it more likely to clot. In the legs, clotting can cause swelling. If the clot is in the lung, you might experience shortness of breath.
- Pleural Effusion A tumor can also mean that abnormal fluid builds up in the sac that surrounds the lungs, leading to breathing problems.
- Neutropenia, or low level of white blood cells
- Lymphedema, or swelling caused by a buildup of lymph fluids
- Hair loss
- Cognitive issues
- Cancer pain from surgery, radiation-induced tissue damage, or chemotherapy
- Blood clots
- Depression
- Sexual dysfunction
While discussing treatment with you, a doctor will explain the benefits and risks of each option, allowing you to make an informed decision about balancing the effects of treatment on cancer with its complications and side effects. The doctor will also consider ways to manage these, such as pain-relieving medications, mental health support, and other treatments.
Support for People With Cancer
This national organization provides free professional support services from specialized social workers, including counseling, support groups, and cancer education workshops. CancerCare also offers limited financial assistance for treatment-related costs such as transportation, home care, and childcare, along with a searchable database of other financial resources.
Through webinars and state-specific resources, Triage Cancer provides guidance on the practical, financial, and legal issues that can arise after a cancer diagnosis. It also offers a Legal and Financial Navigation Program that provides one-on-one assistance with health and disability insurance, employment rights, and estate planning.
This free worldwide service offers one-on-one peer support by matching Support Seekers - people with cancer, caregivers, survivors, and those who carry a genetic cancer risk - with Mentor Angels. These mentors are cancer survivors or caregivers who have faced similar diagnoses and life situations.
The Takeaway
- Cancer develops when abnormal cells in your body grow uncontrollably, forming tumors that invade healthy tissue. Cancer is a common disease. Due to medical advances, there are many more people living with cancer now than ever before.
- Regular screenings can detect some cancer early, improving your chances of survival, so speak to your doctor about which cancer screenings are suitable for you.
- Diagnosis often involves a biopsy, scans, or blood tests. Treatment usually involves a combination of surgery, chemotherapy, radiation therapy, and other options. These can cause a range of side effects, but your cancer care team will explain the risks and benefits.
- Anyone can get cancer, but certain risk factors like smoking, sun exposure, and family history can increase your chances. Managing risk factors and staying on top of routine screenings can help you catch cancer early, when it's most treatable.
FAQ
Resources We Trust
- Mayo Clinic: Cancer Prevention: 7 Tips to Reduce Your Risk
- Cleveland Clinic: 9 Best Ways To Support Someone Who’s Going Through Cancer Treatment
- National Cancer Institute: Cancer Statistics
- American Cancer Society: Support and Online Communities
- Cancer Research Institute: Cancer Clinical Trials
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- Blood Cancer. Cleveland Clinic. April 15, 2025.
- Lymphoma. Cleveland Clinic. June 9, 2023.
- Types of Brain and Spinal Cord Tumors in Adults. American Cancer Society. January 5, 2026.
- Neuroendocrine tumors. Cleveland Clinic. June 26, 2024.
- Cancer. Mayo Clinic. November 19, 2024.
- The Genetics of Cancer. National Cancer Institute. August 8, 2024.
- Radon and Cancer Risk. American Cancer Society. January 16, 2026.
- Understanding Family Cancer Syndromes. American Cancer Society. September 14, 2022.
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- The American Cancer Society Guideline for Cervical Cancer Screening. American Cancer Society. December 4, 2025.
- Endoscopy. American Cancer Society. February 23, 2026.
- Cancer Grade vs. Cancer Stage. MD Anderson Cancer Center.
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- Cryotherapy for Retinoblastoma. American Cancer Society. September 11, 2025.
- Hyperthermia Therapy. Cleveland Clinic. April 29, 2022.
- Laser Treatment. Cancer Research UK. February 25, 2025.
- Radiation Therapy. Cleveland Clinic. September 7, 2022.
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- Stem Cell & Bone Marrow Transplantation. MD Anderson Cancer Center.
- Cancer and Complementary Health Approaches: What You Need To Know. National Center for Complementary and Integrative Health. October 2021.
- Cannabis During Cancer Treatment. Dana Farber Cancer Insititute.
- Cancer Disparities. National Cancer Institute. January 31, 2025.
- Cancer Prevention: 7 Tips to Reduce Your Risk. Mayo Clinic. November 23, 2024.
- Understanding Cancer Prognosis. National Cancer Institute. May 29, 2024.
- Some Complications of Cancer. MSD Manuals Consumer Versions.
- High Calcium Levels (Hypercalcemia). Canadian Cancer Society.
- Cancer and the Risk of Blood Clots. Cancer Research UK. April 24, 2025.
- Side Effects of Cancer Treatment. Centers for Disease Control and Prevention. August 26, 2024.
- Are Your Patients With Cancer Experiencing Sexual Dysfunction? Just Ask! Cleveland Clinic. April 29, 2025.
- How Can Cancer Kill You? Cancer Research UK.

Tawee Tanvetyanon, MD, MPH
Medical Reviewer
Tawee Tanvetyanon, MD, MPH, is a professor of oncologic sciences and senior member at H. Lee Moffitt Cancer Center and Morsani College of Medicine at the University of South Florida in Tampa. He is a practicing medical oncologist specializing in lung cancer, thymic malignancy, and mesothelioma.
A physician manager of lung cancer screening program, he also serves as a faculty panelist for NCCN (National Comprehensive Cancer Network) guidelines in non-small cell lung cancer, mesothelioma, thymoma, and smoking cessation. To date, he has authored or coauthored over 100 biomedical publications indexed by Pubmed.

Adam Felman
Author
As a hearing aid user and hearing loss advocate, Adam greatly values content that illuminates invisible disabilities. (He's also a music producer and loves the opportunity to explore the junction at which hearing loss and music collide head-on.)
In his spare time, Adam enjoys running along Worthing seafront, hanging out with his rescue dog, Maggie, and performing loop artistry for disgruntled-looking rooms of 10 people or less.