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NIH MedlinePlus the Magazine, Trusted Health Information from the National Institutes of Health

Breast Cancer

Breast Cancer Basics and You: Introduction

A woman with a pensive look of her face

According to the National Cancer Institute (NCI), there were more than 194,000 new cases of breast cancer in the United States in 2009. More than 40,000 people died of the disease. It occurs in both men and women, although male breast cancer is rare.

The Breasts

Inside a woman's breast are 15 to 20 sections called lobes. Each lobe contains many smaller sections called lobules. These are groups of tiny glands that make breast milk. Breast milk flows through thin tubes called ducts to the nipple. Fat and other tissue fills the spaces between the lobules and ducts. The breasts also contain lymph vessels, which are connected to small, round masses of tissue called lymph nodes. Lymph nodes produce cells that help the body fight infection. Groups of lymph nodes are near the breast in the underarm, above the collarbone, and in the chest behind the breastbone.

The lobes and ducts of the breast, and nearby lymph nodes (above) are areas that cancer can attack

The lobes and ducts of the breast, and nearby lymph nodes (above) are areas that cancer can attack. The temporary inconvenience of a mammogram (opposite page) can save you from troublesome and costly treatment and surgery by catching breast cancer early, when it is easiest to treat.

Cancer Cells

Cancer begins in cells, the building blocks of body tissues. Cells grow and divide to form new cells. When normal cells grow old or get damaged, they die, and new cells take their place. Sometimes, new cells form when the body doesn't need them, and old or damaged cells don't die as they should. The extra cells often form a mass of tissue called a lump, growth, or tumor. Breast tumors can be benign (not cancer) or malignant (cancer).

Benign tumors:

  • are rarely a threat to life
  • can be removed and usually don't grow back
  • don't invade the tissues around them
  • don't spread to other parts of the body

Malignant tumors:

  • may be a threat to life
  • often can be removed but sometimes grow back
  • can invade and damage nearby organs and tissues (such as the chest wall)
  • can spread to other parts of the body

Breast cancer cells can break away from the original tumor and enter blood vessels or lymph vessels, which branch into all the tissues of the body. The cancer cells may spread to lymph nodes near the breast, or they may attach to other tissues, growing into new, damaging tumors.

Risk Factors

No one knows what causes breast cancer. Risk factors for breast cancer include age, personal and family health history, genetic changes, prior radiation therapy, reproductive and menstrual history, race, breast density, overweight and obesity, physical inactivity, and alcohol consumption. You can avoid some risk factors, such as drinking alcohol. Having a risk factor does not mean that you will get breast cancer. Most women with risk factors never develop breast cancer.


Early breast cancer usually doesn't cause symptoms. But as the tumor grows, it can change how the breast looks or feels, including:

  • A lump or thickening in or near the breast or underarm area
  • A change in the size or shape of the breast
  • Dimpling or puckering in the skin of the breast. The skin may be ridged or pitted like an orange.
  • A nipple turned inward into the breast
  • Fluid discharge from the nipple, especially if it's bloody
  • Scaly, red, or swollen skin on the breast, nipple, or areola (the dark area of skin at the center of the breast)

See your healthcare provider about any of these symptoms that do not go away.

Spring / Summer 2010 Issue: Volume 5 Number 2 Page 17