Every time tissue is removed from the body looking for cancer, it is sent to a pathologist for evaluation under a microscope. Over 90% of biopsies performed of the breast reveal benign breast tissue.

The pathologist looks for changes in the normal cells in the breast. Most breast cancers start in the ducts or lobules of the breast. When cancer cells are seen, the pathologist evaluates the cells to see where they are growing. Non-invasive cancer cells stay inside the ducts and lobules. These are called in situ cancers. Because they have not spread, they are almost always cured with local treatments (surgery, radiation). Some people refer to in situ cancers as pre-cancers. Several terms describe these pre-cancers including atypical ductal hyperplasia, ductal carcinoma in situ and lobular carcinoma in situ.

Invasive cancers grow from inside the ducts and lobules into the surrounding normal breast tissues. Invasive cancer can spread to other parts of the body through blood vessels and lymphatics. The pathologist looks for invasion of blood vessels, lymphatics, and nerves under the microscope.

There are several histologic types of invasive breast cancer that the pathologist uses to describe the appearance of the cancer cell. They include ductal (most common breast cancer), lobular, medullary, colloid, papillary, tubular, inflammatory, mucinous, undifferentiated, squamous, adenocystic, Paget’s disease, secretory, cribriform.

The grade of the cancer cells describes how similar the cancer cells are to normal cells:

• Grade 1 (low grade/well differentiated): Slowly growing cancer cells that look similar to normal cells.
• Grade 2 (moderate grade/moderately differentiated): Cancer cells do not look like normal cells and grow faster than grade 1.
• Grade 3 (high grade/poorly differentiated): Cancer cells have few similarities to normal cells. They grow fast.

Additional special tests for cell markers are also performed that help with treatment options. Hormone receptors are on the surface of the cell membranes. Hormones attach to the receptor to change the growth activity of the cells. Breast cancer cells are tested for estrogen and progesterone receptors. ER-positive and PR-positive tumors respond to hormone medications. They are taken in pill form on a daily basis for up to five years.

HER-2 receptors on cancer cell membranes indicate faster growing cells with increased risk of spread. HER-2 positive cancers can be treated with a drug, Herceptin, that binds to and shuts down the HER-2 receptors, stopping growth of the cancer cell.

More advanced testing of the cancer cells’ genetic makeup can also be performed in specific situations to aid in treatment decisions.

Breast Cancer Staging
Breast cancers are staged based on the size of the tumor and the involvement of the axillary nodes. Staging helps your doctors determine the best treatment options. Higher stage cancers usually receive more aggressive treatments with chemotherapy or radiation therapy.

Breast cancers are staged: 0, I, II (A or B), III (A, B or C), or IV.

• Stage 0: Carcinoma in situ (ductal, lobular or Paget’s)
• Stage I: Tumor size 2 cm or less with no involved axillary lymph nodes.
• Stage II
  • Tumor over 2 cm, equal or less than 5 cm, with no involved axillary lymph nodes
  • Tumor over 2 cm, equal or less than 5 cm, with 1 to 3 involved axillary lymph nodes.
• Stage III
  • 4 to 9 involved axillary lymph nodes.
  • Tumor involves skin, chest wall or edema of the skin.
  • 10 or more involved axillary lymph nodes.
• Stage IV: Tumor found elsewhere in the body other than breast or axillary lymph nodes.