After discovering that you have breast cancer, your doctor will decide what additional tests may be helpful to find out if the disease has spread outside the breast. Called breast cancer staging, this process provides information about the extent of the disease.

Your breast cancer stage helps your doctor determine which treatments are most likely to benefit you.

The stages of breast cancer are indicated using Roman numerals ranging from 0 to IV, with 0 indicating cancer that is noninvasive or contained within the milk ducts. Greater numerals indicate a more invasive cancer. By stage IV breast cancer, also called metastatic breast cancer, the cancer has spread to other areas of the body.

The cancer staging system continues to evolve and is becoming more complex as doctors improve cancer diagnosis and treatment.

Your doctor determines your breast cancer stage by considering:

• The size of your tumor
• Whether cancer cells have spread to lymph nodes under your arm (axillary lymph nodes)
• Whether cancer cells have spread to other parts of your body
• How aggressive your cells appear when viewed under a microscope (tumor grade)
• Whether your cancer cells have receptors for the hormones estrogen and progesterone
• Whether your cancer cells have a gene mutation that causes them to make excess HER2 protein
• Results of gene expression profiling tests (Oncotype DX, MammaPrint, others)

To gather information about your cancer, your doctor uses a variety of sources, including:

• Physical exam. To gather the necessary information, your doctor will ask questions about your medical history, do a careful physical examination and review all the tests you've had. This can also include a review of the results from the biopsy of the tumor or suspicious area.
• Pathology report. If you've already had surgery to remove your cancer and nearby lymph nodes, your doctor will use your pathology report to help determine your stage and plan your treatment.
• Tests that evaluate your cancer cells. Cells from your cancer, collected during a biopsy procedure or during surgery to remove the cancer, are tested in a laboratory to help determine the aggressiveness of the cells and whether they are sensitive to hormones. Other sophisticated tests can determine what gene mutations are present in the cells. Not all of these tests are necessary in every case. Your doctor will help determine which tests are needed based on your particular situation.
• Blood tests. No blood test can tell you your cancer stage, but blood tests may give your doctor an idea of your overall health and clues about which other staging tests may be useful. Blood tests might include a complete blood count and a blood chemistry test, which assess your kidney and liver function.
• Breast-imaging tests. Mammogram, ultrasound and breast MRI give your doctor more information about your cancer and help determine if additional imaging tests may be necessary.

• Additional imaging tests. Additional imaging can be used to look for breast cancer cells that have spread to other areas of your body. Not everyone with breast cancer needs these tests, though, so ask your doctor what's best for you.

  Additional imaging tests include a bone scan, computerized tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET).

Most people with a new diagnosis of breast cancer don't need all the diagnostic tests available. Your doctor will select the necessary tests based on your situation. Particularly if your cancer is small and hasn't spread to nearby lymph nodes, additional tests may offer little benefit, but lead to additional costs and carry a risk of complications.