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NCCN Guidelines for Patients


Breast Cancer - Early-Stage


, Version 1.2016

Breast cancer

Cancer is a disease of cells. Carcinomas are cancers

of cells that make up the skin and the tissue that

lines or covers organs. Almost all breast cancers are

carcinomas. In the breast, carcinomas start in the

cells lining either the ducts or lobules, but most breast

cancers start in ductal cells.

Inside of cells are coded instructions for building

new cells and controlling how cells behave. These

instructions are called genes. Genes are a part

of DNA (






cid), which is grouped

together into bundles called chromosomes.


Figure 1.3.

Abnormal changes (mutations) in

genes cause normal cells to become cancer cells.

Researchers are still trying to learn what causes

genes to mutate and cause cancer.

Cancer cells don’t behave like normal cells in three

key ways. First, mutations in genes cause normal

cells to grow more quickly and live longer. Normal

cells grow and then divide to form new cells when

needed. They also die when old or damaged as

shown in

Figure 1.4

. In contrast, cancer cells make

new cells that aren’t needed and don’t die quickly

when old or damaged. Over time, breast cancer cells

form a mass called the primary tumor.

The second way cancer cells differ from normal

cells is that they can grow into surrounding tissues.

If not treated, the primary tumor can extend beyond

the walls of lobules or ducts into the stroma. Breast

cancers that haven’t grown into the stroma are called

“noninvasive breast cancer.” Breast cancers that have

grown into the stroma, such as stages I and II, are

called “invasive breast cancer.”

Third, unlike normal cells, cancer cells can leave the

breast and form tumors in other parts of the body.

This process is called metastasis. In this process,

cancer cells break away from the tumor and merge

with blood or lymph. Then, the cancer cells travel

in blood or lymph through vessels to other sites.

The first site is your axillary lymph nodes. Common

distant sites include your bones, lungs, brain, and

liver. Once cancer cells are in other sites, they can

form secondary tumors and may cause major health



Breast cancer basics

Breast cancer