Stage 0

Used to describe non-invasive breast cancers, such as DCIS (ductal carcinoma in situ). 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 neighbouring normal tissue.

Stage 1

Describes invasive breast cancer (cancer cells are breaking through to or invading normal surrounding breast tissue).

In general, stage 1A describes invasive breast cancer in which:

• the tumor measures up to 2 cm and
• the cancer has not spread outside the breast; no lymph nodes are involved

In general, stage 1B describes invasive breast cancer in which:

• there is no tumor in the breast; instead, small groups of cancer cells — larger than 0.2 mm but not larger than 2 mm — are found in the lymph nodes or
• there is a tumor in the breast that is no larger than 2 cm, and there are small groups of cancer cells — larger than 0.2 mm but not larger than 2 mm — in the lymph nodes

Still, if the cancer is estrogen-receptor-positive or progesterone-receptor-positive, it is likely to be classified as stage 1A. Microscopic invasion is possible in stage 1 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 2

Divided into subcategories known as 2A and 2B.

In general, stage 2A describes invasive breast cancer in which:

• no tumor can be found in the breast, but cancer (larger than 2 mm) is found in 1 to 3 axillary lymph nodes (the lymph nodes under the arm) or in the lymph nodes near the breastbone (found during a sentinel node biopsy) 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

Still, if the cancer tumor measures between 2 and 5 cm and:

• has not spread to the lymph nodes or parts of the body away from the breast
• is HER2-negative
• is hormone-receptor-positive
• it will likely be classified as stage 1B.

Similarly, if the cancer tumor measures between 2 and 5 cm and:

• has not spread to the lymph nodes
• is HER2-negative
• is estrogen-receptor-positive
• is progesterone-receptor-negative
• has an Oncotype DX Recurrence Score of 9
• it will likely be classified as stage 1A.

In general, stage 2B describes invasive breast cancer in which:

• the tumor is larger than 2 cm but no larger than 5 centimeters; small groups of breast cancer cells — larger than 0.2 mm but not larger than 2 mm — are found in the lymph nodes or
• the tumor is larger than 2 cm but no larger than 5 cm; cancer has spread to 1 to 3 axillary lymph nodes or to lymph nodes near the breastbone (found during a sentinel node biopsy) or
• the tumor is larger than 5 cm but has not spread to the axillary lymph nodes

Still, if the cancer tumor measures between 2 and 5 cm and:

• cancer is found in 1 to 3 axillary lymph nodes
• is HER2-positive
• estrogen-receptor-positive
• progesterone-receptor-positive
• it will likely be classified as stage 1B.

Stage 3

Stage 3 is divided into subcategories known as 3A, 3B, and 3C.

In general, stage 3A describes invasive breast cancer in which either:

• no tumor is found in the breast or the tumor may be any size; cancer is found in 4 to 9 axillary lymph nodes or in the lymph nodes near the breastbone (found during imaging tests or a physical exam) or
• the tumor is larger than 5 cm; small groups of breast cancer cells (larger than 0.2 mm but not larger than 2 mm) are found in the lymph nodes or
• the tumor is larger than 5 cm; cancer has spread to 1 to 3 axillary lymph nodes or to the lymph nodes near the breastbone (found during a sentinel lymph node biopsy)

Still, if the cancer tumor measures more than 5 cm across and:

• is grade 2
• cancer is found in 4 to 9 axillary lymph nodes
• is estrogen-receptor-positive
• is progesterone-receptor-positive
• is HER2-positive
• it will likely be classified as stage 1B.

In general, stage 3B describes invasive breast cancer in which:

• the tumor may be any size and has spread to the chest wall and/or skin of the breast and caused swelling or an ulcer and
• may have spread to up to 9 axillary lymph nodes or
• may have spread to lymph nodes near the breastbone

Still, if the cancer tumor measures more than 5 cm across and:

• is grade 3
• cancer is found in 4 to 9 axillary lymph nodes
• is estrogen-receptor-positive
• is progesterone-receptor-positive
• is HER2-positive
• it will likely be classified as stage 2A.

Inflammatory breast cancer is considered at least stage 3B. Typical features of inflammatory breast cancer include:

• reddening of a large portion of the breast skin
• the breast feels warm and may be swollen
• cancer cells have spread to the lymph nodes and may be found in the skin

In general, stage 3C describes invasive breast cancer in which:

• there may be no sign of cancer in the breast or, if there is a tumor, it may be any size and may have spread to the chest wall and/or the skin of the breast and
• the cancer has spread to 10 or more axillary lymph nodes or
• the cancer has spread to lymph nodes above or below the collarbone or
• the cancer has spread to axillary lymph nodes or to lymph nodes near the breastbone

Still, if the cancer tumor measures any size and:

• is grade 2
• is estrogen-receptor-positive
• is progesterone-receptor-positive
• is HER2-positive or negative
• it will likely be classified as stage 3A.