Breast cancer is staged from 0 to IV, with each stage describing how large the tumor is, whether it has reached nearby lymph nodes, and whether it has spread to distant organs. Staging determines treatment options and helps predict outcomes. The system used by doctors assigns a stage based on three factors: tumor size (T), lymph node involvement (N), and whether the cancer has metastasized (M). Biological markers like hormone receptor status and HER2 status also factor into the final stage assignment.
Stage 0: Non-Invasive Breast Cancer
Stage 0 is the earliest possible diagnosis. The most common form is ductal carcinoma in situ (DCIS), where cancer cells are confined inside a milk duct and have not spread into surrounding breast tissue. Because the cells lack the ability to break out of the duct, stage 0 is considered non-invasive or pre-invasive. It is not life-threatening on its own, but without treatment it can progress to invasive cancer over time.
Stage 0 is typically discovered on a mammogram before any lump can be felt. Treatment usually involves removing the abnormal tissue, sometimes followed by radiation to reduce the chance of recurrence.
Stage I: Small Tumor, Minimal Spread
Stage I means the cancer is invasive but still small and largely contained. It is divided into two sub-stages:
- Stage IA: The tumor is up to 20 millimeters (about the size of a peanut) and has not spread to any lymph nodes.
- Stage IB: Small clusters of cancer cells (between 0.2 and 2 millimeters) are found in the lymph nodes, with either no tumor in the breast or a tumor no larger than 20 millimeters.
Stage I breast cancer has an excellent outlook. When cancer is caught at a localized stage, before it reaches the lymph nodes or distant organs, the five-year relative survival rate is effectively 100%, based on data from the National Cancer Institute’s SEER database covering 2016 to 2022.
Stage II: Larger Tumor or Lymph Node Involvement
Stage II cancers are bigger than stage I or have started to involve nearby lymph nodes, but have not yet reached distant parts of the body. This stage also has two sub-categories:
- Stage IIA: No tumor is found in the breast but cancer is present in one to three underarm lymph nodes, or the tumor is 20 millimeters or smaller and has spread to one to three underarm lymph nodes, or the tumor is between 20 and 50 millimeters with no lymph node involvement.
- Stage IIB: The tumor is between 20 and 50 millimeters and has spread to one to three underarm lymph nodes, or the tumor is larger than 50 millimeters but has not reached any lymph nodes.
Stage II is still considered an earlier stage with strong treatment outcomes. Surgery, radiation, chemotherapy, or hormone-blocking therapy may be used depending on the tumor’s biology. The SEER database groups stages I and II under “regional” when lymph nodes are involved, where the five-year relative survival rate is 87.5%.
Stage III: Locally Advanced Breast Cancer
Stage III means the cancer has spread more extensively within the breast area, reaching multiple lymph nodes, the chest wall, or the skin of the breast, but it has not traveled to distant organs. This is called locally advanced breast cancer, and it includes three sub-stages with increasingly wider spread.
Stage IIIA
The cancer may be any size (or not detectable in the breast at all) and has spread to four to nine lymph nodes under the arm or to lymph nodes near the breastbone. Alternatively, the tumor is larger than 50 millimeters and has reached one to three underarm lymph nodes or the lymph nodes near the breastbone.
Stage IIIB
The cancer has grown into the chest wall or the skin of the breast, causing visible changes like skin breakdown (ulceration) or swelling. It may have spread to up to nine lymph nodes in the armpit or to lymph nodes near the breastbone. Inflammatory breast cancer, a fast-growing form that causes the breast to become red, swollen, and warm, is always classified as at least stage III at diagnosis because the cancer cells have already grown into the skin.
Stage IIIC
The tumor can be any size, and it may or may not have reached the chest wall or skin. What defines this sub-stage is extensive lymph node involvement: cancer in 10 or more underarm lymph nodes, in lymph nodes above or below the collarbone, or in both the underarm and breastbone lymph nodes simultaneously.
Treatment for stage III typically involves a combination of chemotherapy before surgery (to shrink the tumor), surgery, radiation, and targeted therapies based on the cancer’s biological profile.
Stage IV: Metastatic Breast Cancer
Stage IV means the cancer has spread beyond the breast and nearby lymph nodes to distant organs. This is metastatic breast cancer, and it can be diagnosed at the initial finding or develop years after treatment for an earlier stage. The most common sites where breast cancer spreads are the bones, lungs, liver, and brain.
Metastatic breast cancer is treatable but not considered curable with current therapies. The goal of treatment shifts toward controlling the cancer’s growth, managing symptoms, and maintaining quality of life for as long as possible. The five-year relative survival rate for distant-stage breast cancer is 33.8%, though individual outcomes vary widely depending on where the cancer has spread, how it responds to treatment, and its biological characteristics.
How Biomarkers Affect Your Stage
Staging is not based on tumor size and spread alone. Doctors also test the cancer cells for three key biomarkers: estrogen receptors, progesterone receptors, and a protein called HER2. These markers reveal what is driving the cancer’s growth and directly influence the final stage a patient receives. Two people with the same size tumor and the same lymph node involvement can be assigned different stages based on their biomarker results. A tumor that is hormone receptor-positive, for example, tends to behave less aggressively and may be assigned a lower prognostic stage than a similar-sized tumor that tests negative for all three markers (called triple-negative breast cancer).
These biomarkers also guide treatment decisions. Hormone receptor-positive cancers respond to therapies that block estrogen, while HER2-positive cancers can be treated with drugs that target that specific protein. Triple-negative cancers have fewer targeted options, though newer treatments continue to expand what is available.
What the Survival Numbers Actually Mean
Five-year survival rates describe the percentage of people who are alive five years after diagnosis compared to the general population. They are population-level averages drawn from thousands of cases, not predictions for any individual. The numbers also reflect patients diagnosed several years ago, so they don’t fully capture improvements in treatment that have happened since.
The SEER database, maintained by the National Cancer Institute, groups survival data into three broad categories rather than individual stages. Localized cancer (confined to the breast) has a five-year survival rate of 100%. Regional cancer (spread to nearby lymph nodes) sits at 87.5%. Distant cancer (metastatic) is 33.8%. These figures cover all breast cancer subtypes together, so someone with a more treatable subtype like hormone receptor-positive cancer may have better odds than the average, while someone with a more aggressive subtype may face a tougher path.