Breast cancer is a cancer that starts in breast tissue. It happens when cells in the breast change and grow out of control. The cells usually form a tumor.

Sometimes the cancer does not spread any further. This is called "in situ." If the cancer spreads outside the breast, the cancer is called "invasive." It may just spread to nearby tissues and lymph nodes. Or the cancer may metastasize (spread to other parts of the body) through the lymph system or the blood.

Breast cancer is the second most common type of cancer in women in the United States. Rarely, it can also affect men.

There are different types of breast cancer. The types are based on which breast cells turn into cancer. The types include:

• Ductal carcinoma, which begins in the cells of the ducts. This is the most common type.
• Lobular carcinoma, which begins in the lobules. It is more often found in both breasts than other types of breast cancer.
• Inflammatory breast cancer, in which cancer cells block lymph vessels in the skin of the breast. The breast becomes warm, red, and swollen. This is a rare type.
• Paget's disease of the breast, which is a cancer involving the skin of the nipple. It usually also affects the darker skin around the nipple. It is also rare.

Breast cancer happens when there are changes in the genetic material (DNA). Often, the exact cause of these genetic changes is unknown.

But sometimes these genetic changes are inherited, meaning that you are born with them. Breast cancer that is caused by inherited genetic changes is called hereditary breast cancer.

There are also certain genetic changes that can raise your risk of breast cancer, including changes in the BRCA1 and BRCA2 genes. These two changes also raise your risk of ovarian and other cancers.

Besides genetics, your lifestyle and the environment can affect your risk of breast cancer.

The factors that raise your risk of breast cancer include:

• Older age
• History of breast cancer or benign (noncancer) breast disease
• Inherited risk of breast cancer, including having BRCA1 and BRCA2 gene changes
• Dense breast tissue
• A reproductive history that leads to more exposure to the estrogen hormone, including
  • Menstruating at an early age
  • Being at an older age when you first gave birth or never having given birth
  • Starting menopause at a later age
• Taking hormone therapy for symptoms of menopause
• Radiation therapy to the breast or chest
• Obesity
• Drinking alcohol

The signs and symptoms of breast cancer include:

• A new lump or thickening in or near the breast or in the armpit.
• A change in the size or shape of the breast.
• A dimple or puckering in the skin of the breast. It may look like the skin of an orange.
• A nipple turned inward into the breast.
• Nipple discharge other than breast milk. The discharge might happen suddenly, be bloody, or happen in only one breast.
• Scaly, red, or swollen skin in the nipple area or the breast
• Pain in any area of the breast.

Your health care provider may use many tools to diagnose breast cancer and figure out which type you have:

• A physical exam, including a clinical breast exam (CBE). This involves checking for any lumps or anything else that seems unusual with the breasts and armpits.
• A medical history.
• Imaging tests, such as a mammogram, an ultrasound, or an MRI.
• Breast biopsy.
• Blood chemistry tests, which measure different substances in the blood, including electrolytes, fats, proteins, glucose (sugar), and enzymes. Some of the specific blood chemistry tests include a basic metabolic panel (BMP), a comprehensive metabolic panel (CMP), and an electrolyte panel.

If these tests show that you have breast cancer, you will have tests that study the cancer cells. These tests help your provider decide which treatment would be best for you. The tests may include:

• Genetic tests for genetic changes such as in the BRCA and TP53 genes.
• HER2 test. HER2 is a protein involved with cell growth. It is on the outside of all breast cells. If your breast cancer cells have more HER2 than normal, they can grow more quickly and spread to other parts of the body.
• An estrogen and progesterone receptor test. This test measures the amount of estrogen and progesterone (hormones) receptors in cancer tissue. If there are more receptors than normal, the cancer is called estrogen and/or progesterone receptor positive. This type of breast cancer may grow more quickly.

Another step is staging the cancer. Staging involves doing tests to find out whether the cancer has spread within the breast or to other parts of the body. The tests may include other diagnostic imaging tests and a sentinel lymph node biopsy. This biopsy is done to see whether the cancer has spread to the lymph nodes.

Treatments for breast cancer include:

• Surgery such as
  • A mastectomy, which removes the whole breast
  • A lumpectomy to remove the cancer and some normal tissue around it, but not the breast itself
• Radiation therapy
• Chemotherapy
• Hormone therapy, which blocks cancer cells from getting the hormones they need to grow
• Targeted therapy, which uses drugs or other substances that attack specific cancer cells with less harm to normal cells
• Immunotherapy

You may be able to help prevent breast cancer by making healthy lifestyle changes such as:

• Staying at a healthy weight
• Limiting alcohol use
• Getting enough exercisee
• Limiting your exposure to estrogen by
  • Breastfeeding your babies if you can
  • Limiting hormone therapy

If you are at high risk, your health care provider may suggest that you take certain medicines to lower the risk. Some women at very high risk may decide to get a mastectomy (of their healthy breasts) to prevent breast cancer.

It's also important to get regular mammograms. They may be able to identify breast cancer in the early stages, when it is easier to treat.

NIH: National Cancer Institute