After a breast cancer diagnosis, oncologists and breast surgeons stage the cancer. Breast cancer staging describes the extent of cancer in the body. Doctors look at the size of the tumor, whether cancer cells have spread the lymph nodes under the arm, and whether cancer cells have spread to other parts of the body. 

The breast cancer stage at diagnosis determines prognosis and guides treatment. Generally, lower stages have better prognoses and survival rates than higher stages. In fact, the 5-year survival is 98% at the earliest stage, when cancer is small and confined to the breast. Here’s a summary of the stages:

Stage 0 

Stage 0 is ductal carcinoma in situ (DCIS). DCIS is the earliest form of breast cancer and is noninvasive: cancer cells are growing inside the milk ducts, but remain in place (in situ).

Stage 0 treatment usually involves surgery because the cancer is confined to the breast. Breast-conserving surgery (lumpectomy) or mastectomy are options. [8,10] In some cases, doctors recommend adding hormone therapy or radiation.

Stage I 

Stage I includes early forms of invasive breast cancer. The cancer has invaded other breast tissue, but tumors are small, measuring less than 2 cm—less than an inch in diameter. There are two subcategories, IA and IB. 

Stage IA: 

  • Tumor is confined to the breast 
  • Cancer cells have not spread. There is no to the lymph nodes involvement and no metastasis to other sites in the body. 

Stage IB: 

  • Small groups of breast cancer cells are present in local lymph nodes. Local lymph nodes are those closest to the breast, usually in the underarm area.

Stage I treatment typically starts with local therapy—surgery and radiation. A lumpectomy or mastectomy are usually options. Doctors typically recommend adjuvant therapy, which is treatment after surgery to kill any surviving cancer cells. This can include chemotherapy, hormone therapy, or immune-targeted therapy.

Stage II

Stage II also includes early forms of invasive breast cancer. The tumor is either larger than Stage I or the cancer has spread to local lymph nodes. There are two subcategories, IIA and IIB: 

Stage IIA breast cancer includes one of following:

  • No tumor in the breast, but cancer is in one to three local lymph nodes 
  • Tumor measures 2 cm or less with cancer in local lymph nodes 
  • Tumor measures 2-5 cm with no cancer in the lymph nodes

Stage IIB breast cancer includes one of the following:

  • Tumor measures 2-5 cm with cancer in one to three local lymph nodes 
  • Tumor is larger than 5 cm with no cancer in the lymph nodes

Stage II treatment is similar to Stage I. It starts with local therapy, and then adjuvant therapy afterwards. For women with larger tumors, neoadjuvant therapy is sometimes an option. Neoadjuvant therapy is treatment before surgery to shrink the tumor size. This may allow for breast-conserving surgery instead of a mastectomy.

Stage III

Stage III is locally advanced breast cancer. The cancer has spread to nearby lymph nodes and tissues, but has not spread to distant body sites. There are three subcategories, IIIA, IIIB and IIIC:

Stage IIIA breast cancer includes one of the following: 

  • Any size tumor or no tumor in the breast, with cancer in 4 to 9 local lymph nodes  
  • Tumor larger than 5 cm with cancer in one to three local lymph nodes

Stage IIIB breast cancer includes one of the following: 

  • Tumor has grown into the chest wall with up to 9 lymph nodes affected
  • Tumor has grown out to the skin with up to 9 lymph nodes affected 

Stage IIIC breast cancer includes one of the following: 

  • No tumor in the breast, but cancer has spread to more than 10 local lymph nodes or to more distant lymph nodes
  • Any size tumor in the breast that has also spread to more than 10 local lymph nodes or to more distant lymph nodes
  • Any size tumor in the breast that is invading the chest wall or skin and is also in 10 or more local lymph nodes or other lymph nodes farther away from the breast, such as above or below the collar bone