What is breast cancer?

Frisbie Memorial Hospital - October 21, 2022

To understand breast cancer, it is first important to understand exactly what cancer is: the production of abnormal cells.

Your body is programmed to routinely replenish cells in different organs. As normal cells age or get damaged, they die off and new cells take their place; this is what’s supposed to happen. Abnormal cell growth refers to a buildup of extra cells. This happens when new cells form even though the body doesn’t need them or when old, damaged cells don’t die off.

These extra cells slowly accumulate to form a malignant (or cancerous) tissue mass, lump or growth called a tumor. These abnormal cells can destroy normal body tissue and spread through the bloodstream and lymphatic system.

Breast cancer starts in the breasts, but it can spread to other parts of your body if it isn’t caught at an early stage. When cancer cells form, they can break away from where the tumor is located and travel into your blood vessels or lymph vessels (vessels connected to small masses of tissue called lymph nodes). From your vessels, these malignant cells can attach to other tissues and grow into new tumors.

Breast cancer can be ductal carcinoma (cancer that starts in the breast ducts—the system that carries breast milk from the lobules to the nipple) or lobular carcinoma (cancer that starts in the breast lobules — the glands of the breast that produce milk).

If you have been diagnosed with breast cancer, you know that your healthcare team is very important throughout your journey. This group of supporters may include your oncologists, surgeon, nurse navigator, a dietitian, a social worker or other medical professionals. Every member plays an important role.

During the staging process of your cancer, you will learn that the TNM staging system is used for all types of cancers, not just breast cancer. The letters TNM describe the amount of cancer and how much it has spread throughout your body.

T: indicates how big the tumor is and whether the cancer has spread into surrounding tissue.
N: indicates whether the cancer has spread to surrounding lymph nodes.
M: indicates metastasis, which means that cancer has spread to other body parts.

Using TNM, your doctor will diagnose your cancer according to one of the following stages:

Stage 0

This is an extremely early stage where abnormal cells are present. They may be in the lining of a breast duct, for example, but there has been no spread.

Stage 1

Stage 1 is an early stage where cancer cells are in the breast tissue but have not spread beyond the breast. The tumor is not more than two centimeters across.

Stage 2

Breast cancer is in Stage 2 when the tumor is less than two centimeters in size but has spread to the lymph nodes under the arm, is between two and five centimeters and has spread or when it is more than five centimeters, but hasn’t spread.

Stage 3

This stage is called locally advanced cancer. The cancer has spread from where it began into nearby tissue and lymph nodes.

Stage 4

This stage refers to a tumor of any size that has spread to other parts or areas of the body beyond the breast and nearby lymph nodes. These areas may include lungs, distant lymph nodes, bones or brain.

Learn more about breast cancer through Sarah Cannon, the global cancer institute of HCA.