NCCN Guidelines for Patients® | Stages I and II Breast Cancer - page 9

NCCN Guidelines for Patients
Stages I and II Breast Cancer, Version 1.2014
Breast cancer basics
Breast cancer
Cells have a control center called the nucleus.
The nucleus contains special molecules called
chromosomes. Within chromosomes are coded
instructions, called genes, for building new cells and
controlling how cells behave. Changes in genes,
called mutations, cause normal breast cells to
become cancer cells. Cancer cells don’t behave like
normal cells in three key ways.
First, the changes in genes cause cancer cells to
make too many copies of themselves. Normal cells
divide and multiply when new cells are needed, but
otherwise live in a resting state. Normal cells also die
when old or damaged. 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 extend beyond
the walls of lobules or ducts into the stroma. Breast
cancers that have grown into the stroma, such as
stages I and II, are called “invasive.”
Third, unlike normal cells, cancer cells can break off
from the primary tumor and form secondary tumors.
Secondary tumors may form in the breast or in other
parts of the body. Breast cancer can spread to other
body parts through blood or lymph vessels that are in
the stroma.
Most often, breast cancer spreads through lymph.
Lymph is a clear fluid that gives cells water and food.
It also has white blood cells that fight germs. Lymph
nodes filter lymph and remove the germs. Most of
the lymph in the breast drains to the axillary lymph
nodes found inside the armpit.
See Figure 2.
Once in
the axillary nodes, cancer cells can multiply and form
secondary tumors.
Figure 1. Parts of the breast
Derivative work of Breast Anatomy by Patrick J. Lynch and C. Carl Jaffe,
MD, available at
scheme.png under a Creative Commons Attribution 3.0 Unported license.
Illustration Copyright © 2014 Nucleus Medical Media, All rights reserved.
Illustration Copyright © 2014 Nucleus Medical Media, All rights reserved.
Figure 2. Axillary lymph nodes
1,2,3,4,5,6,7,8 10,11,12,13,14,15,16,17,18,19,...96
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