Once upon a time, diagnosing breast cancer was a straightforward matter of yes or no. But research has since uncovered details of breast cancer cells and tissue that can offer valuable guidance for treatment.
That's why, after you're diagnosed with breast cancer, your doctor will probably recommend one or more tests to get more information. 
Many of these tests are done in a laboratory. Others are imaging tests, which may be uncomfortable but shouldn't hurt. 
Laboratory tests
These tests are done on tissue samples taken from the tumor. According to the <a href="[BASEDOMAIN]/healthinfo/bouncelink.aspx?shortcut=cancersoc" target="_blank">American Cancer Society</a> (ACS), laboratory tests done on breast cancer tissue can include:
Tissue grading. Doctors look at a sample of cancer tissue under a microscope to check for specific features, such as how similar cancer cells are to normal breast cells, the number of cancer cells that are in the process of dividing and the way cancer cells are arranged. 
Breast cancer tends to progress more quickly if the cancer cells are very different from normal cells, if a large number of the cancer cells are dividing or if the cancer cells are grouped chaotically.
Tests to see if hormones help the cancer grow. If hormones do seem to help the tumor expand, treatment with certain drugs or removal of the ovaries&mdash;which supply hormones&mdash;may help slow the tumor's growth. 
Tumors that respond to hormones tend to be slower-growing than tumors that aren't sensitive to hormones.
A Ki-67 test to get an idea of how quickly cancer cells are dividing. This is an important predictor of how aggressive the cancer will be.
HER2/neu testing to look for a protein that makes tumors grow more quickly. About 1 in 5 breast cancers have too much of this protein, according to the ACS. These tumors can be treated with medicines that interfere with the protein's action.
Genetic testing to determine how likely the cancer is to recur or come back after initial treatment. This test may be used to decide how aggressively to treat a small breast cancer that shows no sign of having spread.
Imaging tests
If there's any chance that the cancer has spread beyond the breast, your doctor may recommend imaging tests to check for signs of cancer in other parts of the body. These tests can include:
A chest x-ray, which may reveal cancer that's spread to the lungs.
A bone scan, in which mildly radioactive material is injected into a vein and then a special scan is done. The scan shows areas of bone where the radioactive material has collected, a sign of diseased cells.
A computerized tomography (CT) scan, which combines x-ray images taken from several angles to produce a detailed image of a particular area of the body. CT scans can also be used to help guide a biopsy needle to get a tissue sample from an area where cancer may be.
Magnetic resonance imaging (MRI), which produces a detailed, 2D image of internal tissues and structures. MRIs can be especially useful for examining the brain and spinal cord.
Positron emission tomography (PET), which uses a special camera to scan the entire body after a weak radioactive solution is injected into a vein. Cancer cells absorb more of the solution than normal cells. Because it can scan the entire body at once, this test is often used if a doctor suspects that the cancer has spread but doesn't know which organs it may have spread to. 
After testing
Based on the results of your tests, your doctor will recommend a plan to treat your cancer.
Make sure to ask questions about anything you don't understand regarding your test results or the treatment plan. You may also want to consider seeking a second opinion before you start treatment. 
Reviewed 10/29/2023

Tests you'll need after you've been diagnosed with breast cancer

All breast cancers aren't treated the same way. Testing can help your doctor find out more about the cancer, so he or she can make specific treatment recommendations.