Slide show: Stages of breast cancer
Illustration of tissues in breast
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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 based on the amount of breast cancer tissue removed during a mastectomy or lumpectomy and the number of cancer-containing lymph nodes under your arm.

Your breast cancer stage takes into account how large your tumor is and whether your cancer has spread beyond your breast. Using this information, your doctor assigns a Roman numeral — I through IV — that describes your breast cancer stage.

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