Staging takes place after a breast cancer diagnosis is made. Staging of cancer is based on tumor size, lymph node involvement, and whether the cancer has spread (metastasis), according to the American Cancer Society. Treatment and prognosis are determined based on these results, which makes accurate staging an important part of diagnosis.
Stage 0 (Carcinoma in Situ)
Stage 0 breast cancer is also called carcinoma in situ, according to the American Cancer Society. Ductal carcinoma in situ (DCIS) is the earliest form of breast cancer, and means that cancer cells are in a duct, but have not broken through the duct into the breast tissue. Lobular carcinoma in situ may be called Stage 0, but in general, it is not considered actual breast cancer by many oncologists, although it is a risk factor for later breast cancer.
Stage I
The National Cancer Institute defines Stage I breast cancer as a tumor that is 2cm or less, but that has not spread to other organs or lymph nodes.
Stage II
The second stage of breast cancer is classified into two sub-stages: Stage IIA and IIB. Stage IIA breast cancer denotes three circumstances: breast cancer that is in the lymph nodes of the armpit, though there is no breast tumor; a tumor that is less than 2cm and has spread to the lymph nodes in the armpit; or a tumor that is between 2cm and 5cm but has not spread to any lymph nodes. Stage IIB is diagnosed when the tumor is between 2cm and 5cm and there is cancer in the lymph nodes in the armpit, or the tumor is more than 5cm and has not spread to any lymph nodes.
Stage III
Stage III breast cancer has three sub-stages. Stage IIIA describes breast cancer in which there is a tumor 5cm or less, with cancer in four to nine lymph nodes in the armpit, or with enlargement of the mammary lymph nodes; a tumor more than 5cm that is not in the skin or chest wall, and has spread to one to nine lymph nodes, or any lymph nodes in the breast.
Stage IIIB involves a tumor that has grown into the chest wall or skin and is not in the lymph nodes; is in one to three lymph nodes in the armpit with microscopic amounts of cancer in breast lymph nodes on biopsy, or is also in four to nine lymph nodes, or the breast lymph nodes are enlarged. The type of breast cancer called inflammatory breast cancer (IBC) is automatically classified as Stage IIIB; if it has metastasized, it is diagnosed as Stage IV. Stage IIIC breast cancer is characterized by a tumor of any size with 10 or more affected lymph nodes in the armpit; by cancer that has spread to lymph nodes under or over the clavicle; or cancer in four to nine lymph nodes in the armpit as well as in breast lymph nodes upon biopsy.
Stage IV
This is the most advanced stage of breast cancer. Stage IV breast cancer is diagnosed when the cancer has spread to other organs or lymph nodes that are nowhere near the breast, according to the American Cancer Society. The tumor can be any size, and lymph nodes in the armpit may or may not be cancerous. Breast cancer typically spreads to the bone, brain, lungs and liver.
