Breast Cancer Stages: From Stage 0 to IV

Breast cancer staging uses the AJCC system, in its 8th edition, effective since 2018. It measures three things. Tumor size is T. Whether nearby lymph nodes are involved is N. Whether the cancer has spread to distant organs is M. Breast cancer staging goes a step further than many other cancers. It also folds in the tumor's grade. It adds the tumor's estrogen receptor, progesterone receptor, and HER2 status too. Doctors call this combined result the prognostic stage. That is why breast cancer staging can feel more complex than staging for other cancers. The number on your pathology report already accounts for more than just size and spread.

Stage 0 means abnormal cells are present but have not invaded surrounding breast tissue. Doctors call this carcinoma in situ. The most common form is DCIS, or ductal carcinoma in situ. It stays confined to the milk ducts. Because it has not invaded, stage 0 is highly treatable. Some doctors describe it as a precancerous condition rather than true cancer. Even so, most cases are still treated, to prevent it from becoming invasive.

Stage I means the tumor is 2 centimeters or smaller, roughly the size of a peanut. It has not spread to lymph nodes or elsewhere. This is early, localized disease with a generally favorable outlook.

Stage II covers two situations. A tumor between 2 and 5 centimeters falls here, with either no nodes involved or only a small number of nearby nodes. A tumor of 2 centimeters or less also falls here if it has reached a limited number of nearby lymph nodes, and so does a tumor larger than 5 centimeters when no nodes are involved. Once a large tumor and node involvement occur together, the stage moves up to III. Doctors divide stage II into IIA and IIB. The letter depends on the exact combination of size and node involvement.

Stage III means the cancer has grown more extensively within the breast area, without yet reaching distant organs. This can mean more extensive lymph node involvement. It can also mean a tumor that has grown into the chest wall or skin. Doctors divide this into IIIA, IIIB, and IIIC, based on these specific features. Stage III is still treated with the goal of cure. Treatment usually combines surgery, drug treatment, and radiation.

Stage IV means the cancer has spread beyond the breast and nearby lymph nodes to distant organs, most often bone, liver, lungs, or brain. This is also called metastatic breast cancer. It is generally not curable. It is often treatable for years, though, especially when the tumor's molecular subtype responds well to hormone therapy or targeted drugs.

Two tumors can be the exact same size and stage. They can still behave very differently, based on their receptor status. A small tumor that is hormone-receptor-positive and HER2-negative often has an excellent outlook. A similarly sized triple-negative tumor lacks estrogen, progesterone, and HER2 receptors. It tends to be more aggressive. It also has fewer targeted treatment options. This is why your pathology report matters so much, not just your stage number. It is what explains your specific situation.

• What is my exact stage, and what specific factors — size, nodes, receptors — determined it?
• What is my tumor's hormone receptor and HER2 status, and how does that affect my outlook?
• Does an Oncotype DX or similar test apply to my case, and would it change my treatment?
• How will you monitor for recurrence after treatment?

• American Cancer Society — Stages of Breast Cancer
• American Cancer Society — Breast Cancer Treatment