What is breast cancer?
Cancer is a group of diseases that cause cells in the body to change and grow out of control. Most types of cancer cells eventually form a lump or mass called a tumor, and are named after the part of the body where the tumor originates. Breast cancer begins in breast tissue, which is made up of glands for milk production, called lobules, and the ducts that connect the lobules to the nipple. The remainder of the breast is made up of fatty, connective, and lymphatic tissue.

•Most masses are benign--that is, they are not cancerous, do not grow uncontrollably or spread, and are not life-threatening.

•   Some breast cancers are called in-situ because they are confined within the ducts (ductal carcinoma in-situ or DCIS) or lobules (lobular carcinoma in-situ or LCIS) where they originated. Many oncologists believe that LCIS (also known as lobular neoplasia) is not a true cancer, but an indicator of increased risk for developing invasive cancer in either breast.
      ·   The majority of in-situ breast cancers are DCIS, which accounted for about 83% of in-situ
         cases diagnosed during 2004-2008.
    ·   LCIS is much less common than DCIS, accounting for about 11% of female in-situ breast
         cancers diagnosed during 2004-2008.
    ·   Other in-situ breast cancers have characteristics of both ductal and lobular carcinomas or
         have unspecified origins.
•   Most breast cancers are invasive, or infiltrating. These cancers started in the lobules or ducts of the breast but have broken through the duct or glandular walls to invade the surrounding tissue of the breast.
American Cancer Society

Estimated new cases and deaths from breast cancer in the United States in 2019:

New cases: 268,600 (female); 2,670 (male)

Deaths: 41,760 (female); 500 (male)

American Cancer Institute

Breast Cancer Facts

Breast cancer is the most common cancer in women and is second only to lung cancer as the leading cause of cancer deaths among women in the United States. It affects one of every eight American women.

The Center for Disease Control estimates that more than 192,370 women are diagnosed with breast cancer each year, and the number of new cases has declined over the past decade. More than 40,000 women lose their lives to this disease annually.

Men can develop breast cancer, but it happens much less often than in women. Nearly 2,000 men are diagnosed with breast cancer each year.

More on Breast Cancer Types

There are two main types of breast cancer. Breast tumors may have a single type of cancer, a combination of types, or a mixture of invasive and noninvasive (in-situ) cancer.

Ductal carcinoma (cancer) is the most common form of breast cancer. Tumors form in the cells of the milk ducts, which carry milk to the nipples. Ductal carcinoma can be invasive with the potential to spread, or non-invasive (also called ductal carcinoma in-situ or DCIS). About one in five new breast cancer cases are DCIS. The chance for successful treatment of DCIS usually is very high.

Lobular carcinoma (cancer) occurs in the lobules, which are the milk-producing glands. Lobular breast cancer can be non-invasive (in-situ or LCIS, also called lobular neoplasia) or invasive (have a tendency to spread). About one in 10 breast cancer cases are invasive lobular cancer.

Less common types of breast cancer

IBC is a rare, aggressive form of breast cancer that affects the dermal lymphatic system. Rather than forming a lump, IBC tumors grow in flat sheets that cannot be felt in a breast exam. Read more about IBC.
Triple-negative breast cancer is usually an invasive ductal carcinoma with cells that lack estrogen and progesterone receptors and do not have an excess of HER2 protein on their surfaces. These types of breast cancers tend to spread more quickly and do not respond to hormone therapy or drugs that target HER2.
Recurrent breast cancer is cancer that has returned after being undetected for a time. It can occur in the remaining breast tissue or at other sites such as the lungs, liver, bones or brain. Even though these tumors are in new locations, they still are called breast cancer.

MD Anderson

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