Stage is usually expressed as a number on a scale of 0 through IV — with stage 0 describing non-invasive cancers that remain within their original location and stage IV describing invasive cancers that have spread outside the breast to other parts of the body.
Cancer stage is based on four characteristics:
You also may see or hear certain words used to describe the stage of the breast cancer:
Stage 0 is used to describe non-invasive breast cancers, such as DCIS (ductal carcinoma in situ). In stage 0, there is no evidence of cancer cells or non-cancerous abnormal cells breaking out of the part of the breast in which they started, or getting through to or invading neighboring normal tissue.
Stage I describes invasive breast cancer (cancer cells are breaking through to or invading normal surrounding breast tissue) in which the tumor measures up to 2 cm AND no lymph nodes are involved.
Microscopic invasion is possible in stage I breast cancer. In microscopic invasion, the cancer cells have just started to invade the tissue outside the lining of the duct or lobule, but the invading cancer cells can’t measure more than 1 mm.
Stage II is divided into subcategories known as IIA and IIB.
Stage IIA describes invasive breast cancer in which:
no tumor can be found in the breast, but cancer cells are found in the lymph nodes under the arm (axillary) OR
the tumor measures 2 cm or smaller and has spread to the axillary lymph nodes OR
the tumor is larger than 2 cm but not larger than 5 cm and has not spread to the axillary lymph nodes
Stage IIB describes invasive breast cancer in which:
the tumor is larger than 2 cm but no larger than 5 cm and has spread to the axillary lymph nodes OR
the tumor is larger than 5 cm but has not spread to the axillary lymph nodes
Stage III is divided into subcategories known as IIIA, IIIB, and IIIC.
Stage IIIA describes invasive breast cancer in which either:
no tumor is found, but cancer is found in axillary lymph nodes, which are clumped together or sticking to other structures, or cancer may have spread to lymph nodes near the breastbone OR
the cancer is any size and has spread to axillary lymph nodes, which are clumped together or sticking to other structures
Stage IIIB describes invasive breast cancer in which:
Inflammatory breast cancer is considered at least stage IIIB. Typical features of inflammatory breast cancer include:
Stage IIIC describes invasive breast cancer in which:
Stage IV describes invasive breast cancer that has spread beyond the breast and nearby lymph nodes to other organs of the body, such as the lungs, distant lymph nodes, skin, bones, liver, or brain.
You may hear the words “advanced” and “metastatic” used to describe stage IV breast cancer. Cancer may be stage IV at first diagnosis or it can be a recurrence of a previous breast cancer that has spread to other parts of the body.