Diagnosis & Staging

Lumps in the breast, or changes in breast shape, size, or skin qualities can be caused by a myriad of conditions. A positive breast cancer diagnosis can only be achieved through an examination of breast tissue. Thus, biopsies play a critical role in breast cancer diagnoses.

Breast Cancer Staging

Before a diagnosis can be complete, and a treatment course chosen, breast cancer first must be staged. The process determines whether cancer has spread from the breast to other parts of the body. The most commonly used system is the American Joint Committee on Cancer TNM system. In the TNM staging system, cancers are classified based on their T, N, and M stages:

  • T stands for the size of the tumor and how far it has spread within the breast and to nearby organs.
  • N stands for how much it has spread to lymph nodes
  • M stands for metastasis, or how much it has spread to distant organs.

In TNM staging, each letter is associated with a number to indicate some information about the cancer. Once the TNM staging has been determined, this information is combined into a process called “stage grouping.” Stage grouping is the more commonly discussed method of cancer standing, in which stages range from 0 to IV. The lower the number, the earlier the cancer stage.

Stage 0

This stage describes noninvasive (“in situ”) breast cancer. Ductal carcinoma in situ (DCIS) is an example of stage 0 cancer.

Stage I

This stage marks the first identification of invasive breast cancer. At this point, the tumor measures no more than 2 centimeters in diameter (or about 3/4 inch) and there are no lymph nodes involved; the cancer is completely inside the breast.

Stage II

This stage describes invasive breast cancers in which one of the following is true: 

  • The tumor measures less than 2 centimeters (3/4 inch), but has spread to lymph nodes under the arm.
  • The tumor is between 2 and 5 centimeters (about 3/4 inch to 2 inches) and may or may not have spread to lymph nodes under the arm.
  • The tumor is larger than 5 centimeters (2 inches), but hasn't spread to any lymph nodes.
  • No tumor is found in the breast, but breast cancer cells are found in lymph nodes under the arm.

Stage III

These breast cancers are subdivided into three categories (A, B, and C) based on a number of criteria. By definition, Stage III cancers have not spread to distant sites.

  • Stage IIIA tumors are either larger than 5 centimeters (2 inches) and have spread to one to three lymph nodes under the arm, or are any size and have spread into multiple lymph nodes.
  • Stage IIIB tumor of any size has spread to tissues near the breast—the skin and chest muscles—and may have spread to lymph nodes within the breast or under the arm.
  • Stage IIIC cancer is a tumor of any size that has spread: to 10 or more lymph nodes under the arm; to lymph nodes above or beneath the collarbone and near the neck; to lymph nodes within the breast itself and under the arm.

Stage IV

Stage IV breast cancer has spread to distant parts of the body, such as the lungs, liver, bones, or brain.