NCCN Guidelines for Patients
Breast Cancer – Metastatic (STAGE IV), Version 2.2017
Breast cancer basics
A disease of cells
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 (
wrapped around proteins.
See Figure 3.
DNA are coded instructions for building new cells and
controlling how cells behave. These instructions are
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 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
. 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.