What Is Breast Cancer?

Updated 
August 31, 2015
Reviewed By: 

Breast cancer is a group of diseases that occur when normal breast cells grow and reproduce out of control, turning into malignantinfo-icon, or cancerous, cells.

Healthy cells grow and divide to form new cells as the body needs them, and die if they are damaged or old. In cancerous cells, abnormalinfo-icon changes in the genes responsible for cellinfo-icon growth cause them to divide out of control. The malignant cells may form into tumors, or groups of cancer cells. 

Cancer cells, and the tumors they form, can travel either short distances or longer ones to different parts of the body. Researchers are still learning about the different ways cancer spreads. A tumorinfo-icon formed by cells that have spread away from the breast is called metastatic breast cancer or a metastasisinfo-icon.

Breast cancers usually start in the ducts or the lobules of the breast. Breast cancer in the ducts is called ductal cancer and in the lobules is called lobular cancer. The lobules are glands that make breast milk, and the ducts are the passageways that carry the milk from the lobules to the nippleinfo-icon.

To plan treatment, your doctors need to learn about the makeup of the breast cancer. This process begins with a biopsyinfo-icon, when a doctor removes a small amount of your breast tissueinfo-icon. This sample is sent to a pathologistinfo-icon, a doctor who diagnoses diseases by looking at tissues under a microscope. After seeing cancer cells in the sample, your pathologist diagnoses breast cancer.

Tests will tell you what makes the cancer grow, how fast it is growing and whether it has traveled to other areas of your body. The results, which can all be found in your pathology reportinfo-icon, help your doctors select the treatments most likely to benefit you. Learn about the types of tests in our section on Testing.

Invasive vs. Noninvasive Disease

Noninvasiveinfo-icon disease stays inside the ducts or lobules of the breast, where it started. This is called carcinoma in situinfo-icon. Noninvasive disease, as its name says, does not have the ability to travel outside the ducts or lobules of the breast to the lymphinfo-icon nodes and other parts of the body.

Invasive disease grows outside the ducts or lobules of the breast into nearby tissueinfo-icon. It has the potential to travel away from the breast to other areas of the body.

Invasive Ductal Carcinoma

Invasive ductal carcinomainfo-icon, IDC, is sometimes called infiltrating ductal carcinomainfo-icon. It is the most common type of breast cancer, and it accounts for about 80 percent of all breast cancers.

The lobules are glands that make breast milk, and the ducts are the passageways that carry the milk from the lobules to the nippleinfo-icon. IDC starts in the cells that line the ducts. It breaks through the wall of the milk ductinfo-icon and grows outside the ducts. IDC also invades the tissues of the breast and can travel to the lymphinfo-icon nodes. It has the ability to spread, or metastasizeinfo-icon, to other areas of the body.

Diagnosing IDC

A diagnosisinfo-icon of IDC usually begins when you feel a lump or get a routine mammograminfo-icon that shows an abnormality. Your doctor would then do other tests, such as another mammogram, an ultrasound or a breast MRIinfo-icon.

If one or more of these tests suggest you may have cancer, you will have a biopsyinfo-icon, which is how your doctor makes a diagnosis. A biopsy involves removing cells or tissues for a pathologistinfo-icon, a doctor who specializes in diagnosing specific diseases, to look at.

Treating IDC

Treatments for invasive ductal carcinoma include local treatments, such as surgeryinfo-icon and radiation therapyinfo-icon, to control and get rid of the disease in the breast and nearby lymph nodes.

Systemicinfo-icon treatments may also be used to get rid of cancer cells that may have traveled away from the primary, or original, tumorinfo-icon. The goal of systemic therapyinfo-icon in early-stage breast cancerinfo-icon is to reduce the chance of the cancer coming back by getting rid of tiny cells that may have escaped the breast or other areas of the body. It can involve hormonal therapy, chemotherapy and targeted therapy, depending on the type of cancer and your risk for cancer return.

You and your doctor will work together to decide which treatments are best for you. 

Invasive Lobular Carcinoma

Invasive lobular carcinomainfo-icon, or ILC, is cancer that begins in the lobules of the breast and spreads to surrounding tissues. It is the second most common type of breast cancer. Between 10 and 15 percent of breast cancers are ILC.

Diagnosing ILC

A diagnosisinfo-icon of ILC usually begins when you feel a lump or get a routine mammograminfo-icon that shows an abnormality. Your doctor would then do other tests, such as another mammogram, an ultrasound or a breast MRIinfo-icon.

If one or more of these tests suggest you may have cancer, you will have a biopsyinfo-icon, which is how your doctor makes a diagnosis. A biopsy involves removing cells or tissues for a pathologistinfo-icon, a doctor who specializes in diagnosing specific diseases, to look at.

Treating ILC

Though the treatments are often the same, ILC has different qualities and behaves differently than IDC.

Unlike ductal cancers, ILC is more likely to occur in both breasts at the same time, called bilateral breast cancerinfo-icon. ILC tends to respond less than ductal cancers to chemotherapyinfo-icon. Most ILCs are estrogen receptor-positive (ER-positive) and HER2-negative.

You and your doctor will work together to decide which treatments are best for you. 

Staging

Breast cancer has five stages, 0 to IV. Doctors use these stages to predict your chances of survival and to decide which treatments to recommend for you. For example, a stageinfo-icon 0 cancer, or noninvasiveinfo-icon cancer, has an almost 100 percent chance of long-term survival. A stage IV cancer, where the disease has traveled throughout the body, has a lower chance of long-term survival.

These are the five major breast cancer stages:

  • Stage 0 breast cancers are noninvasive, or DCISinfo-icon. They are confined to the ducts of the breast.
  • Stage I breast cancers are invasive. They have grown into tissueinfo-icon outside the ducts or lobules of the breast. Stage I breast cancers are 2 centimeters or smaller and are not in the lymphinfo-icon nodes.
  • Stage II breast cancers are invasive and usually affect lymph nodes. These cancers are larger than 2 centimeters across and can be as large as 5 centimeters. They are put into two groups, A and B, based on size and lymph nodeinfo-icon status.
  • Stage III breast cancers are invasive. These cancers are at least 2 centimeters across, can be larger than 5 centimeters, and may be in the lymph nodes. Sometimes the cancer is in lymph nodes near the breastbone or collarbone, or the nodes are matted (stuck) together. These cancers are put into three groups, A, B and C, based on many factors.
  • Stage IV cancers are invasive. They have grown into tissue outside the ducts or lobules of the breast and traveled to other organs, such as the bones, liver, lungs or brain. If you have this diagnosisinfo-icon, also called metastatic breast cancer, LBBC has tailored services for you.