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NCCN Guidelines for Patients



Breast Cancer – Metastatic (STAGE IV), Version 2.2017


Breast cancer basics

A disease of cells


Cancer’s threat

A disease of cells

Your body is made of trillions of cells. Cancer is a

disease of cells. Each type of cancer is named after

the cell from which it derived. Breast cancer is a

cancer of breast cells.

Almost all breast cancers are carcinomas.

Carcinomas are cancers of cells that make up the

skin and the tissue that lines or covers organs. In

the breast, carcinomas are cancers of cells that line

either the ducts or lobules. Most breast cancers start

in ductal cells.

Cells have a control center called the nucleus.

The nucleus contains chromosomes, which are

long strands of DNA (






cid) tightly

wrapped around proteins.

See Figure 3.


DNA are coded instructions for building new cells and

controlling how cells behave. These instructions are

called genes.

There can be abnormal changes in genes called

mutations. Some types of mutations that are linked

to cancer are present in all cells. Other mutations are

present only in cancer cells. Mutations cause cancer

cells to not behave like normal cells and sometimes

look very different from normal cells.

Cancer’s threat

Cancer cells don’t behave like normal cells in three

key ways. First, cancer cells grow more quickly and

live longer than normal cells. Normal cells grow

and then divide to form new cells when needed.

They also die when old or damaged as shown in

Figure 4

. In contrast, cancer cells make new cells

that aren’t needed and don’t die quickly when old or

damaged. Over time, 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 grow from a duct or

lobule into the stroma. Breast cancers that have

grown into the stroma are called “invasive.”

Third, unlike normal cells, cancer cells can leave

the breast. 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. Once at other sites, cancer cells may form

secondary tumors and cause major health problems.