The extent, or stage, of your breast cancer gives your doctor an idea of your prognosis — the likely outcome of your disease — and helps guide treatment decisions.
Your doctor determines your stage of breast cancer through examination of the tissue removed during a mastectomy or lumpectomy and of the lymph nodes under your arm.
Your breast cancer stage takes into account how large your cancer is and whether it has spread beyond your breast. Using this information, your doctor assigns a Roman numeral — I through IV — that describes your breast cancer stage.
You have stage I breast cancer if all of the following are true:
A stage II breast tumor is larger than a stage I tumor, but the cancer hasn't spread to a distant part of your body. If your cancer is stage II, one of the following is true:
If you have stage III breast cancer, known as locally or regionally advanced cancer, your cancer may have spread to lymph nodes near your breast — those located under your arm or by your collarbone — but not to more-distant parts of your body. Here are some examples:
Inflammatory breast cancer is a form of cancer in which there may be no lump or mass felt in the breast. In inflammatory breast cancer, cancer cells block the lymphatic vessels in breast skin, causing swelling, redness, and ridged or dimpled skin. Inflammatory breast cancer is classified as stage III breast cancer.
Stage IV is the most advanced form of breast cancer. At this stage, breast cancer cells have spread to other areas of your body. Breast cancer most often spreads to the bones, brain, liver and lungs. Stage IV breast cancer is also called metastatic breast cancer.