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This topic is for people who have been diagnosed with breast cancer for the first time. If you are looking for information on breast cancer that has spread or come back after treatment, see the topic Breast Cancer, Metastatic or Recurrent.

What is breast cancer?

Breast cancer occurs when abnormal cells grow out of control in one or both breasts. They can invade nearby tissues and form a mass, called a malignant tumor. The cancer cells can spread (metastasize) to the lymph nodes and other parts of the body.

Breast cancer is many women’s worst fear. But experts have made great progress in treating cancer. If it is found early, breast cancer can often be cured, and it is not always necessary to remove the breast.

What causes breast cancer?

Doctors do not know exactly what causes breast cancer. But some things are known to increase the chance that you will get it. These are called risk factors. The main risk factors for breast cancer include:¹

• Aging. Breast cancer is much more common in older women than in younger women. Your breast cancer risk increases as you age.²
• Family history of breast cancer . You have a higher risk if a close family member, especially your mother or sister, has had breast cancer.
• Female hormones. Using hormone therapy after menopause raises your risk. This includes estrogen-progestin and estrogen-testosterone.^{1, 3} Using estrogen by itself may slightly raise breast cancer risk.¹ And your risk is slightly higher if you started your period before age 12 or started menopause after age 55. The years when you have a menstrual cycle are your high-estrogen years. Experts think that the longer you have higher estrogen, the more risk you have for breast cancer.⁴
• Gene changes. Women who inherit certain genes called BRCA1 and BRCA2 are more likely to have breast cancer.

Some other things are known to increase your risk, such as having extra body fat, being inactive, or drinking alcohol (these lead to higher levels of estrogen in the body).^{4, 5}

But many women who have risk factors do not get breast cancer. And many women who get breast cancer do not have any known risk factors.

What are the symptoms?

Breast cancer can cause:

• A change in the way the breast feels. The most common symptom is a painless lump or thickening in the breast or underarm.
• A change in the way the breast looks. The skin on the breast may dimple or look like an orange peel. There may be a change in the size or shape of the breast.
• A change in the nipple. It may turn in. The skin around it may look scaly.
• A clear or bloody fluid that comes out of the nipple.