How is cancer diagnosed?

Cancer is nearly always diagnosed by an expert who has looked at cell or tissue samples under a microscope. In some cases, tests done on the cells’ proteins, DNA, and RNA can help tell doctors if there’s cancer. These test results are very important when choosing the best treatment options.

Tests of cells and tissues can find many other kinds of diseases, too. For instance, if doctors are not sure a lump is cancer, they may take out a small piece of it and have it tested for cancer and for infections or other problems that can cause growths that may look like cancer.

The procedure that takes out a piece of the lump, or a sample for testing is called a biopsy.

The tissue sample is called the biopsy specimen.

The testing process is sometimes referred to as pathology.

Lumps that could be cancer might be found by imaging tests or felt as lumps during a physical exam, but they still must be sampled and looked at under a microscope to find out what they really are. Not all lumps are cancer. In fact, most tumors are not cancer.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: March 30, 2015 Last Revised: July 30, 2015

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