Definition

Breast cancer is cancer that forms in the cells of the breasts. Breast cancer can occur in both men and women, but it's far more common in women.

After skin cancer, breast cancer is the most common cancer diagnosed in women in the United States. But breast cancer rates have fallen in recent years, though doctors aren't certain why. Still, for many women, breast cancer is the disease they fear most.

Public support for breast cancer awareness and research funding has helped improve the diagnosis and treatment of breast cancer. Breast cancer survival rates have increased and the number of deaths has been declining, thanks to earlier detection, new treatments and a better understanding of the disease.

Symptoms

Signs and symptoms of breast cancer may include:

• A breast lump or thickening that feels different from the surrounding tissue
• Bloody discharge from the nipple
• Change in the size or shape of a breast
• Changes to the skin over the breast, such as dimpling
• Inverted nipple
• Peeling or flaking of the nipple skin
• Redness or pitting of the skin over your breast, like the skin of an orange

When to see a doctor
If you find a lump or other change in your breast — even if a recent mammogram was normal — make an appointment with your doctor.

Causes

It's not clear what causes breast cancer. Doctors know that breast cancer occurs when some breast cells begin growing abnormally. These cells divide more rapidly than healthy cells do. The accumulating cells form a tumor that may spread (metastasize) through your breast, to your lymph nodes or to other parts of your body.

Breast cancer most often begins with cells in the milk-producing ducts. Doctors call this type of breast cancer invasive ductal carcinoma. Breast cancer may also begin in the lobules (invasive lobular carcinoma) or cells within the breast.

Researchers have identified things that can increase your risk of breast cancer. But it's not clear why some people who have no risk factors develop cancer, yet other people with risk factors never do. It's likely that breast cancer is caused by a complex combination of your genetic makeup and your environment.

Inherited breast cancer
Doctors estimate that 5 to 10 percent of breast cancers are linked to gene mutation passed through generations of a family. A number of inherited defective genes that can increase the likelihood of breast cancer have been identified. The most common are breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2), both of which increase the risk of both breast and ovarian cancer.

If you have a strong family history of breast cancer or other cancers, blood tests may help identify defective BRCA or other genes that are being passed through your family. Consider asking your doctor for a referral to a genetic counselor who can review your family health history. A genetic counselor can also discuss the benefits, risks and limitations of genetic testing with you.