Cancer basics

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Over 1.4 million people are expected to be diagnosed with cancer in the United States this year.* Many more are undergoing treatment or living cancer-free after treatment. Learning about cancer can help you better understand your choices.

What is cancer?

Normally your body grows only the new cells it needs. If something damages cells' genes (DNA), they don't die when they should, or they grow quickly and invade other tissues. There are more than a hundred types of cancer.

What's a tumor?

Sometimes extra cells can clump together to form a tumor, or lump of tissue. Not all cancers form tumors.

  • Benign tumors aren't cancerous and don't spread to other body parts. They can often be removed without coming back.
  • Malignant tumors are cancerous, and cells from these tumors can spread. When cancer spreads, it's called metastasis.

What's an oncologist?

An oncologist is a doctor who specializes in treating cancer. There are different kinds of oncologists. Medical oncologists specialize in giving chemotherapy and other treatments. They are usually the doctor that follows you through your treatment and beyond. Radiation oncologists specialize in radiation treatments and a surgical oncologist specializes in performing surgeries for cancer.

*National Cancer InstituteKaiser Permanente is not responsible for the content or policies of external Internet sites, or mobile apps.

Reviewed by Kaiser Permanente in 2018

A shoulder to lean on

Find out about support groups, classes, and other services that can help you cope with cancer.

My health manager

Email your doctor's office, get test results, refill your prescriptions, and more, all from the comfort of your home.

Research and clinical trials

Learn about cancer research and clinical trials at Kaiser Permanente and other organizations.