What is Breast Cancer?

Introduction to Breast Cancer

Breast cancer is the most common cause of cancer in women and the second most common cause of cancer death in women in the U.S. While the majority of new breast cancers are diagnosed as a result of an abnormality seen on a mammogram, a lump or change in consistency of the breast tissue can also be a warning sign of the disease. Heightened awareness of breast cancer risk in the past decades has led to an increase in the number of women undergoing mammography for screening, leading to detection of cancers in earlier stages and a improvement in survival rates. Still, breast cancer is the most common cause of death in women between the ages of 45 and 55. Although breast cancer in women is a common form of cancer, male breast cancer does occur and accounts for about 1% of all cancer deaths in men.

Research has yielded much information about the causes of breast cancers, and it is now believed that genetic and/or hormonal factors are the primary risk factors for breast cancer. Staging systems have been developed to allow doctors to characterize the extent to which a particular cancer has spread and to make decisions concerning treatment options. Breast cancer treatment depends upon many factors, including the type of cancer and the extent to which it has spread. Treatment options for breast cancer may involve surgery (removal of the cancer alone or, in some cases, mastectomy), radiation therapy, hormonal therapy, and/or chemotherapy.

With advances in screening, diagnosis, and treatment, the death rate for breast cancer has declined by about 20% over the past decade, and research is ongoing to develop even more effective screening and treatment programs.

How is the breast designed?

The breasts sit on the chest muscles that cover the ribs. Each breast is made of 15 to 20 lobes. Lobes contain many smaller lobules. Lobules contain groups of tiny glands that can produce milk. Milk flows from the lobules through thin tubes called ducts to the nipple. The nipple is in the center of a dark area of skin called the areola. Fat fills the spaces between the lobules and ducts.

The breasts also contain lymph vessels. These vessels lead to small, round organs called lymph nodes. Groups of lymph nodes are near the breast in the axilla (underarm), above the collarbone, in the chest behind the breastbone, and in many other parts of the body. The lymph nodes trap bacteria, cancer cells, or other harmful substances.

What is breast cancer?

Breast cancer is an abnormal growth of cells that normally line the ducts and the lobules. Breast cancer is classified by whether the cancer started in the ducts or lobules, whether the cells have “invaded” (grown or spread) through the duct or lobule, and the way the cancer cells look under a microscope.

When the cancer is confined in the ducts or lobules of the breast, the cancer is referred to as in-situ or non-invasive. The most common type begins in the lining of the milk ducts and is referred to as “ductal carcinoma in situ”, those that begin in the lobules where breast milk is produced is known as “lobular carcinoma in situ”, and those that have spread beyond the walls of the ducts or lobules (referred to as “infiltrating” or “invasive”). The cells in infiltrating or invasive cancers can enter the blood stream or lymphatic system. Once this happens; the cancer can spread (metastasize) to other parts of the body. The most common area of metastasis is in the lymph nodes under the arm, called axillary lymph nodes. Mestastatis can also be found in other lymph nodes in the body, or more commonly, in the bones, lungs, or liver.

It is not unusual for a single breast tumor to have combinations of these types, and to have a mixture of invasive and non-invasive cancer.

Types of Breast Cancers

Carcinoma In Situ

Carcinoma is another word for cancer and carcinoma in situ (CIS) means that the cancer is a very early cancer and it is still confined to the ducts or lobules where it started. It has not spread into surrounding fatty tissues in the breast or to other organs in the body.

There are 2 types of breast carcinoma in situ:

  • Ductal carcinoma in situ (DCIS): This is the most common type of noninvasive breast cancer. In DCIS, cancer cells inside the ducts do not spread through the walls of the ducts into the fatty tissue of the breast. DCIS is treated with surgery and sometimes radiation, which are usually curative. If not treated, DCIS may grow and become an invasive cancer.
  • Lobular carcinoma in situ (LCIS): Also called lobular neoplasia; not considered to be a true cancer. It begins in the milk-producing glands of the breast lobules, but has not grown through the lobule walls. Breast cancer specialists think that LCIS is thought to be only a risk factor for the future development of breast cancer but women with this condition do run a higher risk of developing an invasive cancer in either breast.

Invasive Breast Cancers

Invasive cancer describes those cancers that have started to grow and have spread beyond the ducts or lobules. These cancers are divided into different types of invasive breast cancer depending on how the cancer cells look under the microscope. They are also grouped according to how closely they look like normal cells. This is called the grade which helps predict whether the woman has a good or less favorable outlook. Outlook is referred to as prognosis.

Mixed Tumors

Mixed tumors describe those that contain a variety of cell types, such as invasive ductal combined with invasive lobular breast cancer. With this type, the tumor is usually treated as if it were an invasive ductal cancer.

Medullary Cancer

This special type of infiltrating ductal cancer has a fairly well-defined boundary between tumor tissue and normal breast tissue. It also has a number of special features, including the presence of immune system cells at the edges of the tumor. It accounts for about 5% of all breast cancer. It can be difficult to distinguish medullary breast cancer from the more common invasive ductal breast cancer. Most cancer specialists think that medullary cancer is very rare, and that cancers that are called medullary cancer should be treated as invasive ductal breast cancer.

Metaplastic Tumors

Metaplastic tumors are a very rare type of invasive ductal cancer. These tumors include cells that are normally not found in the breast, such as cells that look like skin cells (squamous cells) or cells that make bone. These tumors are treated similarly to invasive ductal cancer.

Inflammatory Breast Cancer (IBC)

Inflammatory breast cancer is a special type of breast cancer in which the cancer cells have spread to the lymph channels in the skin of the breast. Inflammatory breast cancer accounts for about 1% to 3 % of all breast cancers. The skin of the affected breast is red, swollen, may feel warm, and has the appearance of an orange peel. The affected breast may become larger, firmer, tender, or itchy. IBC is often mistaken for infection in its early stages.

Inflammatory breast cancer has a higher chance of spreading and a worse outlook than typical invasive ductal or lobular cancer. Inflammatory breast cancer is always staged as stage IIIB unless it has already spread to other organs at the time of diagnosis which would then make it a stage IV (see discussion of stages).

Colloid Carcinoma

This rare type of invasive ductal breast cancer, also called mucinous carcinoma, is formed by mucus-producing cancer cells. Colloid carcinoma has a better outlook and a lower chance of metastasis than invasive lobular or invasive ductal cancers of the same size.

Tubular Carcinoma

Tubular carcinoma is a special type of invasive ductal breast carcinoma. About 2% of all breast cancers are tubular carcinomas. Women with this type of breast cancer have a better outlook because the cancer is less likely to spread outside the breast than invasive lobular or invasive ductal cancers of the same size. The majority of tubular cancers are hormone receptor positive and HER-2 negative.