How is cancer diagnosed?

A cancer diagnosis is nearly always made by an expert looking at cell or tissue samples under a microscope. In some cases, lab tests of the cells’ proteins, DNA, and RNA can help tell doctors if cancer is present. These tests can also help in choosing the best treatment options. Tests of cells and tissues can find many other kinds of diseases, too. For example, if doctors are not sure a lump is cancer, they may have the sample tested for cancer and for infections or other problems that can cause growths that may look like cancer.

The procedure that takes a sample for this testing is called a biopsy, and the tissue sample is called the biopsy specimen. The testing process is sometimes referred to as pathology.

Lumps that might be cancer might be found by imaging (radiology) studies 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 benign (not cancer).

A malignant tumor (cancer) can spread into nearby tissues and even to distant parts of the body. A benign tumor cannot do this.