Cancer staging is a process that helps doctors determine if a cancer has spread, and ranges from stage O to IV.

Stage O.

Memorial Sloan Kettering Cancer Center (MSKCC) says when a woman is diagnosed with stage 0 breast cancer, it means abnormal cells are present but have not spread to nearby tissue. The earliest stage of the disease, stage 0 is highly treatable when detected early. The American Cancer Society (ACS) reports a five-year survival rate of 99% among individuals diagnosed with stage 0 breast cancer.

Stage I.

Stage I indicates tumor cells have spread to normal surrounding breast tissue but are still contained in a small area. Stage IA indicates a tumor is as large as a grape but hasn’t spread to the lymph nodes. Stage IB indicates the tumor may be slightly smaller, but is accompanied by small clusters of cancer cells in the lymph nodes, or no tumor and only small clusters in the lymph nodes. The ACS reports a 99% five-year survival rate for patients diagnosed with stage I breast cancer.

Stage II.

Stage II breast cancer diagnosis indicates the tumor is between 20 millimeters and 50 millimeters. Stage IIB is when the tumor is larger than 50 millimeters, but no lymph nodes are affected. The tumor size may indicate if the cancer is stage IIA or stage IIB. Stage IIA could indicate there is no tumor or a tumor up to 20 millimeters where the cancer has spread to the lymph nodes under the arm. A tumor between 20 and 50 millimeters that hasn’t spread to lymph nodes is also a stage IIA diagnosis. A stage IIB diagnosis indicates the tumor is between 20 and 50 millimeters and has spread to nearby lymph nodes. The five-year survival rate for stage II breast cancer is around 90%.

Stage III.

Stage III breast cancer had a roughly 86% survival rate between 2013 and 2019, with a tumor larger than 50 millimeters that has affected lymph nodes across a wider region. Stage III cancers can be IIIA, IIIB, or IIIC. The American College of Surgeons says stage IIIA indicates any size tumor that has spread to between 4 and 9 lymph nodes or a tumor larger than 5 centimeters that has spread to between 1 and 3 lymph nodes. Stage IIIB is any size tumor where the cancer has spread to the chest wall. A stage IIIC diagnosis is any size tumor that has spread to 10 or more lymph nodes.

Stage IV.

Stage IV, the most advanced form of breast cancer, can be any size, but has spread beyond the breast to other parts of the body, potentially including organs and tissues. The ACS reports a 31% survival rate for this stage. Only 6% of women diagnosed with breast cancer for the first time have reached stage IV.

Staging makes it easier to understand a breast cancer diagnosis. More information about breast cancer staging is available at www.mskcc.org and www.cancer.org.