A short introduction to breast cancer

Breast cancer is a huge subject. A single search on Google for the term will bring up thousands of results, overflowing with information that would take literally years to read. We understand the enormity of it all can be a little overwhelming, so we put together this short guide to cover the basics and hopefully give you a good understanding of what breast cancer is, how it's identified, and what you can do for yourself and your community to stay as healthy as possible. We invite you to read through all of the information on this page and to share it with anyone and everyone you know. And if you have any questions at all, PLEASE don't hesitate to e-mail us — we'll be more than happy to assist!

*For a more comprehensive guide, please visit Breast Cancer Facts & Statistics, on Komen National's website.

Part 1 - The anatomy of the breast

The breast is largely comprised of three components: ducts (green), lobes (blue), and fat, ligaments and connective tissue (pink)

As demonstrated in the diagram, the human breast is largely comprised of three main components:

  • Ducts:  The ducts carry milk from the lobules to the nipple during breastfeeding. Men are equipped with a smaller number of ducts, though they remain undeveloped.
  • Lobes:  Lobes are "bunches" of small spherical, milk-producing sacs called lobules. Lobules (and correspondingly, lobes) are mostly absent in men, and remain undeveloped when present.
  • Fat, ligaments, and connective tissue:  The remnant spaces of the breast are filled with fat, ligaments and connective tissue. While the amount of milk-producing lobules remain largely consistent among women, the amount of fatty tissue in the breast is highly variable and is the determinant factor in the breast's size.

Part 2 - Breast development in women

When children, girls will likely have a small immature patch of breast tissue that won't see much growth until puberty. During puberty, hormones produced by the ovaries and pituitary gland (a part of the brain that controls growth and other glands in the body) cause the breasts to grow. As the breasts grow, the ducts separate and branch out, eventually developing into the mature system of ducts, lobules, and lobes as referenced above.

Adult women have 15 to 20 lobes in each breast [1], and each lobe has 20 to 40 lobules [2] individually attached to branching ducts. Just like a tree, these smaller ducts join together, forming larger ducts as they approach the nipple. There are about ten duct systems in each breast, each with its own opening at the nipple [2].

Though the breast is mature after puberty, the breast tissue remains inactive until pregnancy. During pregnancy, the lobules grow and begin to produce milk. The milk is then released into the ducts so a mother can breastfeed her baby.

Part 3 - Breast development in men

Similar to girls, boys are likely to have an inactive patch of breast tissue throughout childhood. When boys hit puberty however, the influx of testosterone and comparatively lower levels of estrogen cause breast development to halt, resulting in smaller, inactive breasts for most men.

Part 4 - What is cancer?

In a healthy body, natural systems control the creation, growth and death (called apoptosis) of cells. In this cycle of life, cells divide to make new tissue as older cells die.

When tissue is injured (say by a cut on the hand), the body's cell growth regulators react by speeding up cell division to make new tissue in the injured area as fast as possible. When the body has healed, the cell division goes back to the normal pace.

Cancer is a condition where the natural systems do not work right and cells do not die at the normal rate. As a result, there is more cell growth than cell death. Cancer cells divide without their normal control and make a mass of extra tissue.

As a tumor grows, it promotes the growth of new blood vessels (called angiogenesis) to bring in the oxygen and nutrients it needs. Cancer cells can leave the tumor site and travel through the blood stream and lymphatic system (the network connecting lymph nodes throughout the body) to other parts of the body. This process is called metastasis (meh-TAS-ta-sis). In the new site, the cancer cells may again begin to divide too quickly and make new tumors.

Part 5 - What is breast cancer?

Breast cancer occurs when cells in the breast divide and grow without their normal control. Tumors in the breast tend to grow slowly. By the time a lump is large enough to feel, it may have been growing for as long as 10 years. Some tumors, however, are aggressive and grow much faster.

Between 50 and 75 percent of breast cancers begin in the milk ducts, 10 to 15 percent begin in the lobules and a few begin in other breast tissues [4].


1 - Rosen PP. Rosen's Breast Pathology. Philadelphia: Lippincott Williams & Wilkins, 2001.
2 - Osborne MP and Boolbol SK. Chapter 1. Breast anatomy and development, in Harris JR, Lippman ME, Morrow M, Osborne CK. Diseases of the Breast, 4th edition. Lippincott Williams and Wilkins, 2010.
3 - Smith RA, D'Orsi C, Newell MS. Chapter 11. Screening for breast cancer, in Harris JR, Lippman ME, Morrow M, Osborne CK. Diseases of the Breast, 4th edition. Lippincott Williams and Wilkins, 2010.
4 - Dillon DA, Guidi AJ, Schnitt SJ. Chapter 28: Pathology of Invasive Breast Cancer, in Harris JR, Lippman ME, Morrow M, Osborne CK. Diseases of the Breast, 4th edition, Lippincott Williams & Wilkins, 2010.
5 - Centers for Disease Control and Prevention. Breast cancer: Symptoms. http://www.cdc.gov/cancer/breast/basic_info/symptoms.htm, 2012.