What is Breast Cancer?

The breast is made up of ducts terminating in lobules.

Below is a brief summary on breast cancer terms including major types of breast cancer, breast cancer stage and grade, and the significance of hormone receptors in breast cancer.

Breast Structure and Function

In order to better understand breast cancer and subsequent treatment options, it is helpful
to first understand the breast’s basic structure and function. The breast is composed of milk ducts that run like pipes through the breast. At the end of the duct toward the back of the breast, is a bulb-shaped lobe. The Duct/Lobe structure is embedded in and surrounded by fibrous tissue and fatty tissue. Milk is produced in the lobe and runs through the duct to the nipple for the purpose of breast feeding.

What is Breast Cancer?

The entire body is made up of microscopic cells. Healthy cells divide or duplicate in a timely manner to replace older, dying cells. Cancer cells develop when damage to DNA causes cell growth to accelerate and multiply out of control. With breast cancer, the rapid cell growth most often originates inside the milk duct. The second most common origination site is in the lobe. Research has discovered that many breast cancers are influenced by high estrogen levels in breast tissue. But age remains the number one risk factor for breast cancer. As we get older, our DNA is more vulnerable to damage. More often than not, breast cancer is being detected early due to advances in screening and detection, making treatment outcomes quite favorable.

Ductal Carcinoma In Situ (DCIS) – Stage 0

Cells begin to multiply inside the milk duct, which is like a pipe that runs through the breast. More and more breast cancers are detected at this early stage. On a mammogram. DCIS often appears as calcifications which look like little grains of salt. Not all calcifications are suspicious. Calcifications that are round, smooth and evenly distributed are usually benign calcium deposits (a normal finding). Smaller “micro”calcifications with rough jagged edges, grouped together or in a linear pattern are suspicious in appearance. Suspicious microcalcifications are usually recommended for biopsy and may result in a diagnosis of DCIS or invasive breast cancer.

  • DCIS accounts for approximately 20% of newly diagnosed breast disease
  • Ductal (refers to its origin inside the milk duct),
  • Carcinoma (medical term for cancer)
  • In Situ – Latin for In Place (or you can think of it as “In Side”)
  • DCIS is technically a precancerous finding classified as Stage 0.
  • Typically treated by lumpectomy and radiation therapy.
  • If DCIS has traveled throughout the duct system, mastectomy may be necessary to obtain clear margins.

Infiltrating (Invasive) Ductal Carcinoma (IDC)

Approximately 80% of breast cancer is invasive ductal carcinoma making it the most common type of breast cancer. The cells begin to multiply inside the duct and eventually break through the wall of the duct into the breast tissue where they usually form a mass. If untreated, the tumor grows and can progress from Stage I (tumor 2cm or smaller and not involving lymph nodes) to Stage IV (metastasis to other parts of the body).

Infiltrating (Invasive) Lobular Carcinoma (ILC)

Infiltrating Lobular Carcinoma accounts for approximately 10% of invasive breast cancers. Invasive lobular cancer tends not to form a mass which makes it harder to detect by mammography or breast exam. The progression from Stage I to Stage IV is similar to invasive ductal carcinoma.

Tumor Stage

Staging describes the extent of the breast cancer- indicating how far it has progressed. The stage is determined by the size of the tumor (or involvement in the breast) and whether or not it has spread to other parts of the body.

  • Staging is helpful in estimating prognosis, short-term and long-term outcomes
  • Physicians determine the best treatment plan for you based on estimated or known stage.
  • Staging is used to determine eligibility for various clinical trials for which you may be enrolled.

There are 3 basic categories involved in determining the breast cancer stage:

  • Tumor Size (or extent of involvement in the breast)
  • Lymph Node status (spread to nodes in the axilla- or armpit)
  • Metastasis (whether or not cancer cells have spread to other body parts).

TNM is the staging system used by most medical facilities.

CLINICAL STAGE is an estimated stage based on imaging, biopsy and clinical exam. Most references to staging prior to surgery are referred to as the Clinical Stage. One exception is known metastatic disease prior to breast surgery.

PATHOLOGIC STAGE is determined after surgery. Pathologic Stage is the extent of disease based on examination of the surgical specimen.

Tumor Grade

Cancer cells divide and multiply out of control without order or purpose. This rapid growth results in extra tissue or breast mass called a tumor. Tumor grade is a system used to categorize cancer cells according to how abnormal they appear under the microscope.

There are 3 categories:

  • Grade 1: Low Grade or Well Differentiated – meaning that the cancer cell still resembles a normal cell in most respects. Also considered to be slower growing and therefore less aggressive.
  • Grade 2: Intermediate Grade or Moderately Differentiated – these cells are beginning to lose the look and characteristics of a normal cell. Their speed of growth and aggressiveness is accelerating.
  • Grade 3: High Grade or Poorly Differentiated – these cells have lost all order, purpose and appearance of a normal functioning cell. They are categorized as most aggressive but react most favorably to chemotherapy.

Hormone Receptor Status

Several hormones have been found to have an influence on breast cancer growth. Identifying the hormone status of your breast cancer provides additional information that is important in determining your treatment plan.


Testing is conducted to determine whether or not your breast cancer is estrogen receptor positive or negative.

Estrogen Receptor POSITIVE (ER+) means that the cancer cells used estrogen as a fuel source to grow and multiply. ER+ breast cancer is typically less aggressive and responds well to anti-estrogen therapy which blocks the hormone receptors so they can’t signal cancer cells to grow.

Some of the anti-estrogen therapeutic agents used to treat hormone-receptor positive cancers are:

• Tamoxifen
• Arimidex
• Aromasin
• Femara
• Faslodex

ER NEGATIVE (ER-) breast cancer is typically more aggressive and responds better to chemotherapy. Hormonal therapy is not indicated in ER- breast cancer.


Testing of progesterone receptor status is conducted in conjunction with estrogen receptor status, but is of less importance. It is also reported as positive or negative. Both estrogen and progesterone receptor status results are reported on a scale of 0% to 100%, and whether the staining is weak, moderate or strong.


Also called HER2 is an acronym for human epidermal growth factor receptor 2. HER2 is a gene that signals cells to divide, grow and repair. Normal breast cells have 2 copies of the HER2 gene. Breast cancer can occur when a breast cell has more than 2 copies of the gene. The cells begin over producing the HER2 protein. The result is accelerated, uncontrolled cell growth. This genetic malfunction is not inherited. The cause is not yet known. Aging, along with bodily wear and tear most likely plays a role.

HERCEPTIN is an intravenous drug treatment used to treat HER2+ breast cancer. It is used in conjunction with other intravenous chemotherapeutic agents. Her2/neu positive breast cancer is frequently treated with chemotherapy and Herceptin or other targeted medications such as Perjeta prior to surgery.