Cancer: Causes, Symptoms, and Treatment
Medically reviewed by Achuta Uppu, MD, Internal Medicine. Last reviewed: October 23, 2026.
What kind of doctor treats Cancer?
Cancer care starts with your primary care doctor, who can refer you to an oncologist, a doctor who treats cancer with medicine, or a surgeon who removes tumors. Radiation oncologists treat cancer with radiation. A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What is cancer?
Cancer is not just one disease but many diseases. It begins in your cells, the building blocks of your body. Usually the body makes new cells as needed and replaces old ones that die. Sometimes this goes wrong. New cells grow even when the body does not need them, and old cells do not die when they should.
These extra cells can form a lump of tissue called a tumor. A tumor can be benign (not cancer) or malignant (cancer). Cancer is a disease in which some of the body's cells grow uncontrollably and spread to other parts of the body. That spread is called metastasis.
There are more than 100 types of cancer. Most are named for where they start, such as lung cancer or breast cancer. Carcinoma, the most common type, forms in epithelial cells, the cells that cover body surfaces. Leukemia begins in the blood-forming tissue of the bone marrow.
Symptoms
Cancer symptoms depend on the type of cancer. They may include:
- A lump in your breast.
- Blood in your urine or stool.
- Bleeding or bruising for no known reason.
- A sore that does not heal.
- Trouble swallowing.
- A new mole or a change to a mole you already have.
Cancer may cause many symptoms but often does not cause pain. Do not wait for pain before seeing a doctor. See a doctor if symptoms do not get better in a few weeks.
Causes and who gets it
Cancer is a genetic disease. That means changes in your genes cause it. Genes are parts of DNA, the instruction book inside your cells. Only some cancers come from genes passed down from parents. Most gene changes happen during a person's life, from errors as cells divide or from damage by harmful substances, such as chemicals in tobacco smoke and ultraviolet rays from the sun.
The risk of cancer goes up with age, because the body clears damaged cells less well as you get older. Some lifestyle habits may increase your risk of certain types of cancer, such as having obesity and not getting enough physical activity. Smoking, heavy alcohol use, and too much sun may raise the risk of certain cancers.
How doctors diagnose it
There is no single test that can diagnose cancer. Tests are usually based on your symptoms. A doctor may ask about your medical and family history, do a physical exam, and order blood tests or imaging tests (scans that take pictures inside the body). To find out if you have cancer, the doctor may order a biopsy, which removes and examines tissue, cells, or fluids from your body.
Treatment
Treatment depends on the type of cancer and how advanced it is. Most treatment plans may include surgery, radiation, and/or chemotherapy. Some plans involve hormone therapy, immunotherapy, other biological therapy, or stem cell transplantation. Treatment differs from person to person.
When to see a doctor
See a doctor for blood in your urine or stool, a sore that does not heal, or a new or changed mole. Get care quickly for trouble swallowing that is getting worse. Call 911 for severe chest pain, sudden trouble breathing, or sudden weakness on one side of the body.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor usually charges more and often works alongside insurance. Such a doctor can order early screening tests and follow up on symptoms that do not go away. They can also coordinate care with cancer specialists.
Common questions
Can cancer be prevented?
Not all cancer can be prevented, but you can lower your risk of many common kinds. Avoid smoking, too much sun, heavy alcohol use, and being inactive. Screening tests can find some cancers early, and the HPV test can help prevent cervical cancer.
What screening tests find cancer early?
Tests can find breast, cervical, colorectal (colon), and lung cancers early. Screening means checking your body for cancer before you have symptoms. Mammograms are the best way for many women to find breast cancer early. The HPV test and Pap test help prevent or find cervical cancer. Yearly low-dose CT scans are advised for some people at high lung cancer risk.
What is metastasis?
Metastasis is when cancer cells break away and spread to other parts of the body. Treatment at the metastatic stage often aims to control the cancer.
Does a lump always mean cancer?
No. Tumors can be benign or malignant. Benign tumors are not cancer and do not spread into nearby tissues. Still, any new or growing lump should be checked by a doctor so the cause can be found.
Sources
- National Cancer Institute - What Is Cancer?
- MedlinePlus - Cancer
- Centers for Disease Control and Prevention - Cancer Screening Tests
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
