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Diagnosis & treatment
How the breast is built
Almost every confusing thing about breast cancer makes sense once you know what is actually inside a breast. Why one cancer is called ductal and another lobular. Why the skin can dimple. Why the surgeon checks your armpit. Why a mammogram can be hard to read. It all comes back to the plumbing.
The parts of the breast, and what each one does
A breast is a milk-making gland sitting on top of the chest muscle, packed around with fat. There is no muscle inside the breast itself, which is why exercise changes the chest underneath but not the breast on top of it.
Lobules, the factories
are small sacs that make milk. They are grouped in clusters, rather like a bunch of grapes, and there are roughly fifteen to twenty of these clusters in each breast.
Ducts, the pipes
Ducts are thin channels that carry milk from the lobules to the nipple. Each cluster of lobules drains into its own duct, and those ducts converge on the nipple like tributaries running into a river mouth.
Fat and connective tissue, the packing
Everything else is fat and fibrous tissue. This is what gives a breast its size and shape, and it is why breast size has nothing to do with how much milk-making tissue you have, or with breast cancer risk.
Running through it all are thin fibrous bands called Cooper’s ligaments. They anchor the breast tissue to the skin above and to the chest wall behind, and they are the reason a breast holds its shape rather than pooling. Remember these. They come back later.
The nipple and areola
The nipple is where the ducts open. The is the ring of darker skin around it.
The chest wall behind
Behind the breast sits the pectoral muscle, and behind that the ribs. A breast slides over that muscle, which is part of why a lump that moves freely feels different from one that is tethered.
A diagram of the breast
- Lobules, where milk is made
- Ducts, which carry it to the nipple
- Fat and fibrous tissue
- Lymph nodes in the armpit
- Chest muscle
The armpit, and why lymph nodes matter
Alongside the blood supply, the body runs a second drainage network called the lymphatic system. It carries fluid out of tissues, filters it through small bean-shaped , and returns it to the bloodstream.
Most of the breast drains toward the armpit. That is why the matter so much: if breast cancer cells travel anywhere first, that is usually where they go. It is also why breast tissue itself extends up into the armpit, further than most people expect, and why a lump can appear there.
A works entirely off this piece of anatomy. Inject a small amount of radioactive tracer near the tumor, and sometimes a blue dye as well, follow the drainage, and the first node it reaches is the one worth testing.
Breasts change constantly: age, cycles, pregnancy
There is no single normal breast, and yours is not the same from one month to the next.
- Through the month. Hormones make breast tissue swell and become tender, most often in the week or so before a period. Lumpiness that comes and goes with your cycle is usually just this.
- Through pregnancy and breastfeeding. The lobules grow and multiply, and the breast becomes considerably firmer and larger.
- After menopause. Glandular tissue gradually gives way to fat. Breasts become softer, and they usually become less dense on a mammogram, which makes the images easier to read.
- Between people. Size, shape, and symmetry vary enormously and none of it predicts risk. Most people have one breast slightly larger than the other.
You are not looking for a lump against some textbook picture. You are looking for a change from what is normal for you. That is why knowing your own baseline matters. How to check your own breasts walks through it step by step.
What breast anatomy explains about cancer
Here is the payoff. Six things that sound arbitrary until you know where they come from.
| The thing | The anatomy behind it |
|---|---|
| Ductal versus lobular cancer | Cancer is named for where it started. began in a pipe, began in a milk sac. Lobular tends to spread in thin strands rather than a firm ball, which is why it can be harder to feel and harder to see. |
| What in situ means | is abnormal cells still inside a duct, which have not broken through its wall into the surrounding tissue. The wall is the whole distinction between stage 0 and invasive cancer. |
| Skin dimpling and puckering | Cooper’s ligaments. A tumor growing near one can shorten and tug it, and because that ligament is anchored to the skin, the skin is pulled inward. That is the dimple. |
| A nipple that turns inward | The ducts all converge on the nipple. Something growing behind it can pull it back, in the same way as the dimple, one layer deeper. |
| Nipple discharge from one side | The ducts are open channels to the outside. Something growing inside one can bleed, and that blood has somewhere to go. |
| Why dense breasts hide things | is just the ratio of glandular and fibrous tissue to fat. Fat looks dark on a mammogram. Glandular tissue looks white, and so does cancer. More white tissue means less contrast to see a white tumor against. |
Nobody explains the plumbing before they start using words like ductal, in situ, and sentinel node. Ten minutes with a diagram makes the rest of this site, and most of what you will be told in an appointment, considerably easier to follow.
Where this comes from
- Susan G. Komen, What Is Breast Cancer? patient fact sheet, supplied by Dr. Perkins’ office, for the description of lobules and ducts. komen.org
- American Cancer Society, Breast Cancer
- Breastcancer.org
The diagram is an original schematic drawn for this site. It is simplified and not to scale, and it is not a radiological or surgical reference.
Written for patients and simplified on purpose.