If a diagnosis of breast cancer is made, more tests will be done to better understand and characterize the cancer and to see if it has spread to other parts of the body. Finding out what stage the cancer has reached—“staging” it—determines which of several treatment options will likely be the most effective. Staging tests include some or all of the following: chest X-ray, ultrasound, bone scan, MRI, CT scan, and PET scan.
The stage of a breast cancer is based on the results of these tests as well as the evaluation breast tissue and lymph nodes removed at surgery, whether as a lumpectomy or as a mastectomy.
The American Joint Committee on Cancer (AJCC) staging system classifies cancers based on T, N, and M status,
After the T, N, and M categories are determined, the information is combined to determine the stage. Stage is expressed in Roman numerals from least advanced disease - stage I - to the most advanced disease – stage IV. Of breast cancers, lobular carcinoma in-situ and ductal carcinoma in-situ are considered pre-invasive cancers and are classified as stage 0.
A detailed description of the AJCC staging system is available on the American Cancer Society’s website.